Tailored heterojunctions for efficient thin-film organic solar cells: a photoinduced absorption study

R. Schueppel; K. Schmidt; C. Uhrich; K. Schulze; D. Wynands; J. L. Brédas; B. Maennig; M. Pfeiffer; K. Leo; E. Brier; E. Reinold; H.-B. Bu; P. Baeuerle

doi:10.1117/12.732295

27 September 2007 Tailored heterojunctions for efficient thin-film organic solar cells: a photoinduced absorption study

R. Schueppel, K. Schmidt, C. Uhrich, K. Schulze, D. Wynands, J. L. Brédas, B. Maennig, M. Pfeiffer, K. Leo, E. Brier, E. Reinold, H.-B. Bu, P. Baeuerle

Author Affiliations +

Proceedings Volume 6656, Organic Photovoltaics VIII; 66560G (2007) https://doi.org/10.1117/12.732295
Event: Photonic Devices + Applications, 2007, San Diego, California, United States

Abstract

Recently, we have demonstrated an open circuit voltage of 1.0V and a power conversion efficiency of 3.4% in thin film solar cells, utilizing a new acceptor-substituted oligothiophene with an optical gap of 1.77 eV as donor and C₆₀ as acceptor. Stimulated by this result, we systematically study the energy and electron transfer processes taking place at the oligothiophene:fullerene heterojunction along a homologous series of these oligothiophenes. The heterojunction is modified by tuning the HOMO level using different oligothiophene chain lengths, while the LUMO level is essentially fixed by the choice of the acceptor-type end-groups (dicyanovinyl) attached to the oligothiophene. We study electron transfer at the heterojunction to C₆₀ using photoinduced absorption. The observed transitions are unambiguously identified by TD-DFT calculations. With increasing the effective energy gap of the donor-acceptor pair, charge carrier dissociation following the photoinduced electron transfer is eventually replaced by recombination into the triplet state, which alters the photovoltaic operation conditions. Therefore, the optimum open-circuit voltage of a solar cell is a trade-off between an efficient charge separation at the interface and a maximized effective gap. We conclude that values between 1.0 and 1.1 V for the open-circuit voltage in our solar cell devices present an optimum, as higher voltages were only achieved with concomitant losses in charge separation efficiency.

Citation Download Citation

R. Schueppel, K. Schmidt, C. Uhrich, K. Schulze, D. Wynands, J. L. Brédas, B. Maennig, M. Pfeiffer, K. Leo, E. Brier, E. Reinold, H.-B. Bu, and P. Baeuerle "Tailored heterojunctions for efficient thin-film organic solar cells: a photoinduced absorption study", Proc. SPIE 6656, Organic Photovoltaics VIII, 66560G (27 September 2007); https://doi.org/10.1117/12.732295

ACCESS THE FULL ARTICLE

INSTITUTIONAL
Select your institution to access the SPIE Digital Library.

SELECT YOUR INSTITUTION

PERSONAL
Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.

PERSONAL SIGN IN

No SPIE Account? Create one

PURCHASE THIS CONTENT

SUBSCRIBE TO DIGITAL LIBRARY

50 downloads per 1-year subscription

Members: $195

Non-members: $335 ADD TO CART

25 downloads per 1 - year subscription

Members: $145

Non-members: $250 ADD TO CART

PURCHASE SINGLE ARTICLE

Includes PDF, HTML & Video, when available