This PDF file contains the front matter associated with SPIE Proceedings Volume 11809, including the Title Page, Copyright information, and Table of Contents.

Recent advances in organic solar cells are based on non-fullerene acceptors (NFAs) and come with reduced non-radiative voltage losses (ΔVnr). In this presentation, we show that, by contrast to the energy-gap-law dependence observed in conventional donor:fullerene blends, the ΔVnr values in state-of-the-art donor:NFA organic solar cells show no correlation with the energies of charge-transfer electronic states at donor:acceptor interfaces. By combining temperature-dependent electroluminescence experiments and dynamic vibronic simulations, a unified description of ΔVnr is reached for both fullerene- and NFA-based devices. The critical role that the thermal population of local exciton states plays in low-ΔVnr systems is also highlighted. Another interesting finding is that it is the photoluminescence yield of the pristine materials that defines the lower limit of ΔVnr.

In this talk, I will give a short overview of perovskite solar cells with regards to their opportunities and challenges. Opportunities for performance improvement will be highlighted. Challenges regarding durability will be discussed touching on our work on understanding intrinsic stability of perovskites and meta-stability of perovskite solar cells and strategies for boosting perovskite solar cells’ durability against thermal extremes and humidity. Our perovskite solar cells were the first to exceed the strict requirements of International Electrotechnical Commission standards for thermal cycling damp heat and humidity freeze. Such a major breakthrough represents an important step towards commercial viability.

Organic-inorganic halide perovskite (OIHP) materials at the heart of perovskite solar cells (PSCs) have unique crystal structures, which entail rotating organic cations inside inorganic cages, imparting them with desirable optical, electronic, and defect-tolerance properties. To exploit these properties for PSCs application, the reliable deposition of high-quality OIHP thin films over large areas is critically important. The microstructures and grain-boundary networks in the resulting polycrystalline OIHP thin films are equally important as they control the PSC performance and stability. Fundamental phenomena pertaining to synthesis, crystallization, coarsening, microstructural-evolution, and grain-boundary functionalization involved in the processing of OIHP thin films for PSCs are discussed with specific examples. In addition, the unique mechanical behavior of halide perovskites, and its implication on the reliability of PSCs, are discussed.

Deposition of perovskite layers by the antisolvent engineering technique is one of the most common methods employed in perovskite photovoltaics research. Recently, we developed a general method that allows the fabrication of highly efficient perovskite solar cells by any antisolvent. We demonstrate this method by exploring 14 different antisolvents which we use to fabricate perovskite thin films and devices. By characterising the microstructure, composition and crystalline structure of these films, we identify two key factors that influence the quality of the perovskite active layer: the solubility of the organic precursors in the antisolvent and its miscibility with the host solvent(s) of the perovskite precursor solution. We show that depending on these two factors, each antisolvent can be utilized to produce high performance solar cells with efficiencies up to 22%.

Recently, solution processed hybrid perovskites show intriguing electronic and optoelectronic properties applicable in various device application, and the developing of high quality materials is crucial. In this talk, three related aspects are discussed: 1) Establishing the controllable growth of multi-dimensional, low defect, high-quality perovskite crystals by tailoring the morphology and microstructure, and the particular relationship between structure and optoelectronic properties of perovskite materials; 2) Developing novel film growth process, defects passivation and interface engineering for perovskite materials and solar cells, to achieve high performance photovoltaics with certified efficiency of 24.5%; 3) Unveiling the degradation mechanism of hybrid perovskite films and devices under operational conditions. Corresponding methods are proposed to greatly improve the long-term stability of perovskite solar cells.

Recent advances in organic solar cells (OSCs) based on non-fullerene acceptors (NFAs) come along with reduced non-radiative voltage losses. We show that the non-radiative voltage losses in these state-of-the-art donor:NFA OSCs show no correlation with the energies of charge-transfer electronic states at donor:acceptor interfaces, different from conventional fullerene-based OSCs. Based on a combined temperature-dependent electroluminescence experiments and dynamic vibronic simulations, we have been able to rationalize the low voltage losses in these devices, where we highlight the critical role of the thermal population of local exciton states in decreasing the non-radiative losses. An important finding is that the molecular photoluminescence properties of the pristine materials define the limit of non-radiative voltage losses in OSCs, indicating that it is critical to design high-luminescence-efficiency donor and acceptor materials with complementary optical absorption bands extending into the near-infrared region. We further demonstrate that there is no intrinsic limit for efficient charge separation in OSCs with small non-radiative voltage losses.

Molecular electrical doping is of central technological relevance for organic (opto-) electronics since it allows control of charge carrier density and Fermi level position in organic semiconductors (OSCs). Here, we chose to investigate the doping capability of the n-dopant 1,2,3,4,1′,2′,3′,4′-octaphenylrhodocene (OPR). Using the bulky, strongly reducing metallocene to dope the electron-transport polymer poly{[N,N-bis(2-octyldodecyl)naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5’-(2,2’-bithiophene)} [P(NDI2OD-T2)] leads to an increased bulk conductivity and decreased contact resistance. While the former is due to low-level n-doping of the polymer, trap filling and concomitant charge carrier mobility increase, the latter is caused by an accumulation of OPR at an indium tin oxide (ITO) substrate.

Non-radiative losses to the open-circuit voltage are a primary factor in limiting the power conversion efficiency of organic photovoltaic solar cells. The dominate non-radiative loss is intrinsic to the active layer which, along with the thermodynamic limit to the open-circuit voltage, define the quasi-Fermi level splitting (QFLS). Quantification of the QFLS in organic photovoltaic devices is challenging due to the excitonic nature of photoexcitation and device-related non-radiative losses. In this presentation I will outline an experimental approach based on electro-modulated photoluminescence to quantify the QFLS in organic solar cells. Drift-diffusion simulations are used to verify the accuracy of the method, while state-of-the art PM6:Y6 solar cells are created with varying non-radiative losses. This method quantifies the QFLS in organic photovoltaics, fully characterizing the magnitude of different contributions to the non-radiative losses of the open-circuit voltage.

Recently, Sn perovskite solar cell (Sn PVK PV) are attracting attention. However, the efficiency was still lower than that of Pb perovskite solar cells. Recently, the Sn PVK PVs with efficiency higher than 10% have been reported from several research groups. The crystal defects include the presence of Sn4+, Sn2+ defect, I- defect, the presence of Sn0, the interstitial I- and so on. In order to decrease these defect densities, we have proposed some processes such as addition of Ge2+ ion, introduction of ethylammonium cation into A site, and surface passivation of perovskite grain boundary with diaminoethane dilute solution. Our results on efficiency enhancement (13%) is explained by the conduction and valence band energy level against carrier trap depth. In addition, an inverted SnPb perovskite solar cells with 23.3% efficiency is discussed from the view point of optimization of energy alignment.

In this work, we investigate the ultrafast charge carrier dynamics in the double-layered architecture mixed halide (DHA) perovskite photovoltaic devices by ultrafast pump-probe transient absorption spectroscopy (TAS). The measured TAS results show the perovskite solar cell consists of SnO2/(FAPbI3)1-x(MAPbBr3)x/HTAB has stronger transient absorbance with photoinduced bleaching at 750 nm and photoinduced absorption in the range of 550-700 nm. The lifetime of DHA perovskite observed from TAS is approximately 46 µs in conjunction with the electron injection discovered within the first 150 fs, indicating the charge carriers would be easily extracted. Besides, we measured a high power-conversion-efficiency of the DHA perovskite solar cell (PSC) of 21%. Hence, understanding the ultrafast charge carrier dynamics in PSC by pump-probe TAS provides detailed insights into the advanced working mechanism. The results open a door for the development of high-performance perovskite photovoltaics.

Despite the fast growth of using perovskite materials in solar cells and photo-sensors, there are still many unanswered questions about the processes for their unique electro-optical properties. In this regard, simulation of the material can help for better understanding of the perovskites’ properties. In this study, we have investigated the crystalline structure of methylammonium lead iodide, MAPbI₃, perovskite using the density functional theory (DFT). The majority of DFT modeling of perovskite targets the ground state, at 0 K. Analysis at ground state simplifies several quantum mechanical effects and the model results are enlightening. Yet for practical application at ambient temperature, DFT models must include more physical processes which involve making mathematical simplifications and quantum mechanical assumptions to simplify the computations. Here we delved into the practical implication of the move from theory to practical algorithms and tools, identified the range of current computational implications and limitations, the problems of accurately modeling these substances at room temperature, the computational costs, expected results afforded by DFT models for real, practical materials. We have surveyed the required extensions needed to perform DFT on MAPbI3 which necessarily include the temperature modeling, crystal vibrational and frame deformation, phonon action and the novel characteristics of a free MA cation constrained within a Pb-I structure. The developed algorithm for the DFT analysis of perovskite can then be used as a tool for further study of the effect of various factors on the material properties.

As organic solar cell efficiencies continue to climb to heights that were hard to envision a decade ago they are becoming increasingly attractive for commercial adoption. However, there remains a need to address organic solar cell stability, both intrinsic operational stability as well as physical stability in likely applications, such as flexible power sources. In this talk, we discuss how the thermal relaxation behavior of the polymer semiconductor donor and small molecule acceptor can inform the expected stability of the solar cells. The thermal relaxation is probed in detail using dynamic mechanical analysis. The mechanical behavior is then correlated with the morphological stability of the active layers. We show that organic semiconductors that have a high elastic modulus and glass transition temperature have the greatest morphological stability. Interestingly these systems also show poor miscibility highlighting the relationship between processing, morphology, and stability. In addition, we show how the thermomechanical behavior of polymer: small molecule and polymer: polymer blends dictate film ductility and fracture toughness, which have direct implications on the stability of flexible devices.

In this talk I will discuss key recent developments in the field of OPVs with focus on practical strategies for boosting the overall cell performance. Particular emphasis will be placed on the use of electronic dopants and advanced interlayer technologies for improving the cell’s efficiency and operational stability. Finally, the design and implementation of multi-junction cell architectures will be discussed.

In recent years, organometal halide perovskite based photovoltaics have attracted great interest for their high power conversion efficiency (PCE) potentially at low manufacturing cost. Despite the massive progress made by the community, the long-term performance stability and the manufacturability at large scale remain very challenging. In this work, we demonstrate a stable and scalable architecture for perovskite module fabrication. Thermal evaporation assisted 2-step approach is employed for the 1.53 eV perovskite deposition. For high throughput processing, NiOx by linear reactive sputtering is developed as the inorganic hole transport layer (HTL). PCE of 20% is achieved for the solar cell. Perovskite modules with monolithic series interconnected cells by picosecond laser scribing based on the developed cell stack are also fabricated. Above 80% of the initial efficiency is retained after 1000 hrs of thermal mono-stress at 85°C in N2 atmosphere.

Perovskite/silicon tandem solar cells promise power conversion efficiencies (PCE) beyond the thermodynamic limit of single-junction devices. This potential has been unveiled via several champion devices, however, their actual outdoor performance is yet to be investigated. Here, we fabricate 25 %-efficient two-terminal (2T) monolithic perovskite/silicon tandem solar cells and test them outdoors to reveal the characteristics of these devices specifically in hot and sunny climates, which are the ideal locations to operate such efficient photovoltaic devices. In this article, we summarize our observation on the perovskite/silicon tandem solar cells under actual operational conditions and discuss the lessons we take from our interpretations.

Probing the photovoltaic external quantum efficiency (EQE) at photon energies well below the semiconductor bandgap is an important tool for achieving a better understanding of the contribution of trap and tail states involved in charge generation processes in photovoltaic devices, notably solar cells. In this work, we present an electrical and optical noise-reduced EQE apparatus achieving 100 dB dynamic range. We carefully identify and study several device- and EQE apparatus-related factors limiting the EQE measurement sensitivity. Minimizing these factors allows us to detect photocurrents smaller than a fA, corresponding to EQE signals as small as -100 dB. We use these ultra-sensitive EQE measurements to probe weak sub-bandgap absorption features in organic, inorganic and perovskite semiconductors. In this regard, we directly observe photocurrent-contributing sub-gab trap states in organic solar cells significantly lower in energy than the corresponding charge-transfer state.

The rapid increase in the power conversion efficiency of organic solar cells (OSCs) during the last few years has been achieved through the development of non-fullerene small-molecule acceptors (NF-SMAs). Stability is now becoming a pressing concern. The presentation will discuss how intermolecular interactions govern morphological stability, specifically, how the diffusion of an NF-SMA exhibits Arrhenius behavior with an activation energy that scales linearly with the enthalpic Flory-Huggins interaction parameter. Consequently, the thermodynamically most unstable systems (high interaction parameter) are the most kinetically stabilized. In short, unfavorable interactions can enable stability. The activation energy is shown to scale with the glass transition temperature (Tg) of the NF-SMA and mechanical characteristics of the polymer (elastic modulus) of the polymers [1]. This allows predicting relative diffusion properties and thus morphological stability from simple analytical measurements or molecular dynamic simulations. Unfortunately, the star acceptor Y6 and its analogs have low glass transition temperatures, are highly diffusive and thus yield unstable morphologies. In contrast, IEICO-4F is a stable, high Tg material. The relationship of the Tg to the chemical structure is not yet understood except in the most general terms within a homologous series. The side-chains needed to provide solubility are the enemy of stability. Shorter side-chains are better for stability but often results in difficulties in processing. The impact of the molecular core on the Tg is not yet understood. A new approach to molecular design or novel stabilization strategies are needed if devices are to have high performance and high stability at the same time.

In this talk, we present our methodology for both in-situ and operando X-ray characterization of full PSC device stacks. These methods were developed, in collaboration with researchers at SLAC and NREL, initially to study the device properties of MAPbI3 as a function of temperature. Since then, these methods have been applied to understand the phase stability of mixed A-site PSCs of the form XPbI3 where X = FA, Cs, and/or MA. More recently we have explored tin−lead PSCs devices, to better understand diminished device performance upon thermal treatment. This work showed a stable bulk structure of the perovskite absorber, suggesting that the degradation mechanism is dominated by the surface chemistry. This talk will provide a summary of the operando methods developed as well as a report on these past and more recent results.

Halide perovskite materials have promising performance characteristics for low-cost optoelectronic applications. Photovoltaic devices fabricated from perovskite absorbers have reached power conversion efficiencies above 25 per cent in single-junction devices and 28 per cent in tandem devices. Though widely considered defect tolerant materials, perovskites still exhibit a sizeable density of deep sub-gap non-radiative trap states, which create local variations in photoluminescence that fundamentally limit device performance. These trap states have also been associated with light-induced halide segregation in mixed halide perovskite compositions and local strain, both of which can detrimentally impact device stability5. Understanding the nature of these traps will be critical to ultimately eliminate losses and yield devices operating at their theoretical performance limits with optimal stability. In this talk we outline the distribution and compositional and structural origins of non-radiative recombination sites in (Cs0.05FA0.78MA0.17)Pb(I0.83Br0.17)3 thin films (Doherty, Winchester, et al., Nature, 2020). By combining scanning electron and synchrotron X-Ray microscopy techniques with photoemission electron microscopy (PEEM) measurements we reveal that nanoscale trap clusters are distributed non-homogenously across the surface of high performing perovskite films and that there are distinct structural and compositional fingerprints associated with the generation of these detrimental sites. Finally, we will show how combining our scanning electron diffraction with convolutional neural networks can enable low-dose (~6 e/Å2), high-resolution (4nm) automated structural phase identification in beam sensitive thin-film perovskites. This nanoscale insight will help answer ongoing open questions in the field such as “What are the nanoscale origins of instability in perovskite devices?”, “how important is phase purity for performance?”

Because single crystals (SCs) contain less defects, perovskite solar cells (PeSCs) prepared with SCs should ideally exhibit higher efficiencies. Most of the crystallization methods proposed so far, however, require an interfacial layer to modify the surface property of the substrates to facilitate the diffusion of the precursor ions. The resistance of the interfacial layer, which often also serves as charge transport layers, inevitably increases the series resistance of the solar cells, thereby limiting the performance. Herein, we dope the interfacial layer, which is also a hole-transport layer (HTL) in our cells, with p-type organic molecules to reduce their resistances and find the power conversion efficiencies (PCEs) of the single-crystal PeSCs are significantly improved. At the optimal concentration, the PCE is improved to 14.99%; the champion PCE is up to 15.67%. The results indicate that the HTL play an important role in determining the performance of the single-crystal PeSCs.

Here we present highly efficient, large-area perovskite solar cells (PSCs) where the perovskite active layer is deposited by thermal co-evaporation. The co-evaporated MAPbI3 perovskite films are pinhole-free and uniform over several centimeters, showing low surface roughness, and a long carrier lifetime. The perovskite films’ high-quality lets the fabrication of small area PSCs (0.16 cm2) with PCEs above 20%, high reproducibility in both n.i.p and p.i.n configurations, and an impressive thermal and environmental stability over months. Similarly, the first co-evaporated mini-modules (20 cm2) achieved record PCEs above 18.%. We have also developed colored semi-transparent PSCs and mini-modules. The semi-transparent PSCs achieved PCEs consistently ~16.0% for the wide range of colors realized. Our work represents a significant step towards the development of large-area PSCs and mini-modules and the future commercialization of perovskite technology.

We report a new molecular-level interface engineering strategy using a multifunctional ligand that augments long-term operational and thermal stability by chemically modifying the formamidinium lead iodide rich photoactive layer. The surface derivatized solar cells exhibited high operational stability (maximum powering point tracking at 1 sun) with a stabilized T80 (the time over which the device efficiency reduces to 80% of its initial value of post-burn-in) of ≈5950 h at 40 ºC and stabilized efficiency over 23%. The origin of high device stability and performance is correlated to the nano/sub-nanoscale molecular level interactions between ligand and perovskite layer, which is corroborated by comprehensive multiscale characterization. Chemical analysis of the aged devices showed that interface passivation inhibited ion migration and prevented photoinduced I2 release that irreversibly degrades the perovskite.

Hybrid organic-inorganic perovskites have emerged as one of the most promising materials in photovoltaics. However, their instability under operating conditions hampers their practical application. This stimulates the development of hybrid materials with enhanced stabilities during operation. For this purpose, supramolecular chemistry provides a powerful toolbox for controlling the properties of hybrid materials by purposefully tailoring the noncovalent interactions of the organic components. We have demonstrated the role of supramolecular engineering in templating hybrid perovskite structures through halogen bonding and π-based interactions, as well as host-guest complexation, which has been uniquely assessed by solid-state NMR spectroscopy and NMR crystallography. As a result, we have obtained perovskite solar cells that exhibit superior performances and operational stabilities, highlighting the important role of supramolecular templating in advancing hybrid perovskite photovoltaics.

Polyethylenimine (PEI) layers are used as cathode interlayer to reduce the work function of electrode materials and are frequently applied to organic or perovskite opto-electronic devices. PEI was applied from solution on poly(3,4-ethylenedioxythiophene):polystyrene sulfonate mixture, zinc oxide and graphite. Choice of solvent and residual solvent removal ensure the superior functionality. [1] Furthermore, a single-step formation of a low work function cathode interlayer and n‑type bulk doping from semiconducting polymer/PEI blend solution was observed. [2] [1] S. Bontapalle et al., Adv. Mater. Interface 7 (2020) 2000291. [2] K. Seidel et al., ACS Appl. Mater. Interfaces 12 (2020) 28801.

Greenhouses are a form of highly productive farming that conserves land and water. However, greenhouses use significantly more energy compared with conventional farming. For greenhouse to become an attractive option for environmentally sustainable agriculture there is a need to reduce their energy footprint. Employing semitransparent organic solar cells (ST-OSCs) on greenhouse structures has been proposed as a strategy to significantly reduce the systems energy needs. ST-OSCs are particularly attractive given the opportunity to tune spectral transmittance to generate power and also meet the plants lighting needs. In this talk, we experimentally demonstrate that the ST-OSCs result in negligible crop productivity losses when growing red-leaf lettuce, a popular greenhouse crop. We also show through computational modeling that net-zero energy greenhouses can be achieved using ST-OSCs with 10% efficiency. We expand on this model by coupling the energy model to a detailed plant growth model that accounts for light intensity and spectra on crop yield. We modeled over 60 different ST-OSCs that have unique spectral character and performance. We show that integrating ST-OSCs with greenhouse can increase their net present value by nearly 50% thereby revealing that OSCs can assist in achieving environmentally sustainable greenhouse based agriculture.

One major concern for the commercialization of perovskite photovoltaic technology is the toxicity of lead from the water-soluble lead halide perovskites that can contaminate the environment. Here I will present an abundant, low-cost and chemically robust sulfonic acid cation exchange resins (CERs) based method which can prevent lead leakage in damaged perovskite solar modules under severe weather conditions. CERs exhibit both high adsorption capacity and fast adsorption rate to lead in water due to the large binding energy to lead ions in the mesoporous structure. Integrating the CERs with perovskites at different locations have dramatical influence on how strong they prevent lead leakage. I will present several innovations that can reduce the lead leakage from damaged large-area perovskite solar panels to below 7.0 ppb even in the worst scenario that every sub-module is damaged.

We report materials and device designs of solution-processable organic photodiodes (OPDs) for visible or near-infrared (NIR) light detection compatible with CMOS image sensors (CIS), a large market for photodiodes. OPDs for CIS need to be reliably processable on silicon wafers with conventional methods such as spin coating, to have extremely low dark current even at a couple of negative voltages to utilize high gain read-out circuits, and to be stable under 150–250°C heating to endure module packaging. Those requirements have not been taken into an account for organic photovoltaics (OPVs) development, which assumed large area printing at low processing temperature (<150°C). We selected a conventional structure (p-i-n) with a polymeric hole transport layer (HTL) which we originally made for organic light-emitting diodes (OLEDs). The HTL is free from acids and dopants, contributing to excellent device stability. For visible OPDs, we applied a donor/acceptor blend originally made for OPVs, and obtained an external quantum yield (EQE) of ~85% at 450–700 nm with a dark current of ~10⁻⁷ mA/cm². For NIR OPDs targeting 940 nm, we newly developed NIR absorbing non-fullerene acceptors (NFAs) having a sharp absorption peak at the wavelength to realize high EQE (~80%) and low thermal carriers at dark (~10⁻⁵ mA/cm²). Both type of OPDs retained 70–100% of their original EQEs after thermal annealing at <150°C for two hours. In the presentation video, we will show NIR images obtained from the imaging arrays.

By combining the photovoltaic and electrochemical properties of organo-metal hybrid perovskite materials in a single device, a novel photobattery technology is proposed. Utilising the photovoltaic performance of perovskite materials in combination with lithium ion intercalation reactions, a device with the ability both to convert light to electrochemical energy and store it is demonstrated. The motivation for such a device will be discussed, with its inherent impact in areas such as off-grid energy solutions. The fabrication techniques are described and characterisation techniques common to both photovoltaic and electrochemical disciplines, with their recent results are discussed. Modifications are made to conventional electrochemical coin cells and pouch cells, in order to facilitate optical access to the electrode material. Using in-operando x-ray diffraction and optical probing, the fundamental mechanisms of charge storage and ion conversion are investigated.

Hybrid organo-metal halide perovskite solar cells (PSCs) are promising candidates for next generation photovoltaic device primarily due to their high efficiency, printability and low cost. PSCs have exhibited externally verified power conversion efficiencies (PCE) exceeding 25% outclass from 3.8% in 2009, which have encouraged recent efforts on scalable coating technique in PSCs towards manufacturing. However, devices fabricated by scalable techniques are still lagged the state-of-the-art spin coated devices because the power conversion efficiency (PCE) is highly dependent on the morphology and crystallization kinetics under a controlled environment, and delicate solvent system engineering. In this talk, we present the recent works using in-situ technique to guide the development of high performance PSCs using blade coating technology. (a). Via a laminar air-knife assisted room temperature meniscus coating approach to control the drying kinetics during the solidification process, we recently manufacturing friendly, antisolvent-free room-temperature coating of hysteresis-free PSCs with power conversion efficiency (PCE) of 20.26% for 0.06 cm2 and 18.76% for 1 cm2 devices. Moreover, this approach offers a solid model platform for in-situ UV-vis and microscope investigation of the perovskite film drying kinetics. (b) One step further, based on the widest studied champion perovskite solution system DMF-DMSO, we report air-knife assisted fabrication of perovskite solar cell in AMBIENT condition at high relative humidity of 55±5%. In-depth in-situ time-resolved UV-vis spectrometry is carried out to investigate the impact of solvent removal and crystallization rate, which are proven to be a critical factor on influencing the crystallization kinetics and morphology due to moisture attack. The UV-vis spectrometry also enables accurate determination of wet precursor film thickness – a key parameter for fabrication. Anti-solvent free, high humidity ambient coating of hysteresis-free PSCs with PCE of 21.1% and 18.0% are demonstrated for 0.06 cm2 and 1 cm2 devices, respectively. These PSCs coated in high humidity ambient conditions also show comparable stability with those made in N2 glovebox. (c) The room temperature meniscus coating of high-quality perovskite films incorporated with a multifunctional sulfobetaine based zwitterionic surfactant. Systematic in-situ studies uncover the perovskite crystallization pathway and emphasize the surfactant's synergistic role in film construction, crystallization kinetics modulation, defect passivation, and moisture barrier protection. This strategy is applicable across perovskite compositions and device architectures with the enhanced power conversion efficiencies up to 22%. In addition, this approach significantly improves the stability of perovskite films and devices under different aging conditions.

Perovskite solar cells promise to yield efficiencies beyond 30% by improving the quality of the materials and devices. Electronic defect passivation and suppression of detrimental charge-carrier recombination has been used as a strategy to achieve high performance perovskite solar cells. This strategy often relies on interlayers that may also hinder carrier transfer across interfaces. In addition to interfacial charge transport, very little is known about the role of crystallographic structure on charge carrier transport through the bulk of the material. In this presentation, I will discuss how different crystallographic phases of the perovskite affect charge carrier transport. Interfacial transport across interfaces will be further studied to understand whether crystalline structures or amorphous phases are able to efficiently allow transport out the device. Synchrotron-based characterization techniques, such as grazing incidence x-ray spectroscopy and x-ray fluorescence will be used to understand the structural and chemical composition of the films, whereas intensity-modulated photocurrent spectroscopy will be used to understand transport processes in the devices. We show that the orthorhombic phase of the methylammonium lead iodide perovskite forms along with the tetragonal phase and hinders carrier transport and thus short circuit currents. We also show that the crystal structure of the 2D perovskite used as an interlayer in the perovskite solar cell is crucial to efficient charge extraction.

The organic solar cells (OSCs) have contributed a significant role in photovoltaics by improving its power conversion efficiency (PCE). We have introduced a facile method for transferring thin films to achieve polymer solar cells with stacked structures to enhance the bilayer and ternary solar cells' efficiency. By controlling the swelling/de-swelling properties of Polydimethylsiloxane (PDMS) via solvent treatment, we formed uniform organic films upon the PDMS surface and then transferred them to target substrates.This residue-free and place-lift-off transferring method appear to have great promise in increasing the efficiency of multilayer stacked thin-film OSCs.

We present a high-energy wet-milling grinding method to prepare the NiO NPs at a room temperature and a low-temperature solution-processing method for the intercalation of Cs2CO3 into NiO, resulting in bipolar charge-carrier extraction capability for inverted (p–i–n) and conventional planar (n–i–p) PSCs. In comparison with the corresponding device featuring an HTL of NiO alone, the Cs2CO3-intercalated NiO layer exhibited enhanced electron extraction without sacrificing its hole extraction capability. This new material for bipolar charge-carrier extraction has the potential to serve as an inexpensive, scalable, and environmentally stable interconnection layer for emerging flexible tandem photovoltaic devices.

The solvent-robustness and temporal stability of polyethylenimine (PEI) as an electron extraction layer (EEL) in inverted organic solar cells (OSCs) were studied. For that purpose, a PEI EEL is utilized in inverted OSCs with the archetypal Poly (3-hexylthiophene) (P3HT): [6,6]-Phenyl C61 butyric acid methyl ester (PC60BM) donor:acceptor system. Results show that soaking the PEI film in solvents (1-propanol and/or toluene) does not significantly impact OSC performance or photostability. As verified by X-ray photoelectron spectroscopy (XPS) measurements, the N atoms in PEI interact with indium-tin-oxide (ITO), causing PEI to strongly adhere to the surface of ITO so that potential processing solvents do not dissolve it. Shifts in N bands in the case of PEI on ITO compared to the PEI on glass confirm the presence of a strong physical interaction. In addition, comparing OSCs with fresh PEI and N2-stored PEI demonstrates that the PEI film is very stable over time, and a time gap between PEI deposition and subsequent fabrication processes does not affect OSC performance and photostability. We highlight that the utilization of PEI as a stable and robust EEL facilitates bridging between laboratory discoveries of OSCs with their practical demonstration and gives us considerable latitude in tackling the stringent requirements of OSC manufacturing.

Metal halide perovskites have mixed electronic-ionic conductivity that contributes to intrinsic instabilities under operating conditions of voltage, light and temperature, exacerbated in environmental conditions involving oxygen and moisture. A lack of operando characterization, particularly of buried interfaces, limits rational improvement of perovskite solar cells. This talk will focus on measurement and quantification of relevant charge transfer processes at perovskite interfaces. We employ a new metrology approach to evaluate the electrochemical and spectroelectrochemical behaviors of perovskite interfaces, complemented with a combination of photoelectron spectroscopies and operando x-ray diffraction measurements.

Interfaces play a key role in determining the performance of perovskite semiconductors. This talk will present a discussion on both internal and external interfaces of perovskites. First, I will discuss the characterization and properties of the most significant internal interface - grain boundary in perovskite semiconductors. Following this, I will demonstrate “grain-boundary functionalization” as an effective protocol to mitigate the negative impacts and imparting new functions of perovskite grain boundaries. Then, I will present a novel structure of “interpenetrating interface”, which is formed by an interdiffusion reaction between chemically modified perovskite and charge-transporting-layer. This structure delivers enhanced physical properties and chemical stability, highlighting the importance of external interface design in perovskite semiconductors. Finally, I will present a perspective on future studies of perovskite interfaces towards more efficient and stable optoelectronic devices.

Lead halide perovskites are known for their great potential in high-performance light-harvesting devices. We investigated the exciton recombination properties of 2D perovskites. We resolved two bright (optically allowed) exciton doublets and a dark (optically forbidden) exciton. Particularly, under the inherently strong electron-hole exchange interaction, each bright exciton doublet is split into two orthogonally orienting dipoles with large energy splitting of 2 meV, which is the largest experimental values in two-dimensional semiconductors. Furthermore, we observed an efficient transfer of oscillator strengths from the bright excitons to a dark exciton, which originates from strong spin-mixing between bright and dark excitons induced by external magnetic fields, and the optical emission from the dark exciton is brightened. Our results reveal that the physics on exciton recombination in 2D perovskites is rich, while the optical emission properties can be manipulated by external fields

Organic-inorganic lead halide perovskites have high power conversion efficiency and intriguing physical-chemical aspects that attract attention of the photovoltaic community. Methylammonium lead iodide (MAPI) is an archetypal material for lead halide perovskites and mixed electronic and ionic conductor. In order to investigate the key features of its performance, we have to consider the electronic transport as well as ionic transport properties. In previous study about perovskite interface, ions are responsible for the equilibrium space charge potential due to ion adsorption at the contact area between MAPI and oxide layers. The surface chemistry of oxide (TiO₂ and Al₂O₃) and its interaction with perovskite plays an important role in charge transport in perovskite solar cells. From the perovskite solar cell structure, TiO₂ electron transport layer is being replaced by SnO₂ because of its excellent electrical and optical properties and low-temperature process. Nevertheless, the interfacial effect on charge transport between SnO₂ and MAPI is not well identified. In this study, we investigate the surface chemistry of oxides (SnO₂ and TiO₂) and interface effects between MAPI and oxide layers. We also observed the interaction between SnO₂ and MAPI by using UV-Vis spectroscopy, ICP, XPS and compared it with TiO₂. Additionally, we measured the conductivity to understand the charge transport properties by controlling the contact area of MAPI and SnO₂ interface. To optimize the charge transfer in SnO₂ based solar cell, a comparison between compact SnO₂ layer (prepared by ALD) and composite layer (prepared by spin coating) by using various measurements including external quantum efficiency (EQE) and photoluminescence (PL) was also provided. These physical and optical properties were extended to perovskite solar cells which give us evidence on charge extraction and recombination. Our work will provide a better physical understanding of the perovskite solar cell system.

Cost-effective, fast, and non-destructive, on-site photovoltaic (PV) characterization methods are of interest to PV operators to determine countermeasures against defects causing power loss or against safety problems. Combining the advantages of both methods electroluminescence (EL) and thermography is photoluminescence (PL). With our PL setup, we achieved high resolution luminescence images of large area PV modules without any physical and electrical contact. Defects are recognizable with a high rate compared to indoor EL images at controlled conditions. We analyzed inactive areas, cracks, potential induced degradation, snail trails, EVA degradation, and interconnection failures and compared the PL images with different characterization methods.