Berlin 2015 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 36: Organic Electronics and Photovoltaics: OPV II (joint session CPP, HL, TT)

CPP 36.8: Talk

Wednesday, March 18, 2015, 11:30–11:45, C 130

Morphology Tuning by Side-chain Variation in Bulk-Hetero-Junction Solar Cells Based on Merocyanines — •Dirk Hertel, Julian Nowak, Stephanie Rüth, Ruth Bruker, Jürgen Schelter, and Klaus Meerholz — Universität zu Köln, Department Chemie, Luxemburgerstrasse 116, 50939 Köln

Organic photovoltaics (OPV) offers the potential of mass-produced renewable energy. Within the last decade the efficiency of organic solar cells has increased from 3 % to 10 %, mainly based on better understanding and control of morphology. We investigate merocyanines (MC), a class of low-molecular-weight colorants, as donor material in organic solar cells. These molecules are processable via both deposition techniques showing remarkable power conversion efficiencies (PCE) beyond 4% for SOL- and 6% for VAC-processed devices. Despite these impressive numbers the understanding of the influence of morphology on charge generation, transport and recombination in MCs is in its infancy. To aim towards even higher PCEs we have systematically varied the side-chain of a prototypical donor-acceptor MC with a high ground state dipole moment. By applying atomic-force mircroscopy, transmission electron microscopy and x-ray diffraction we are able to elucidate the thin film structure and show how side-chain variation reduces domain size and improves device data. We are able to correlate crystal size to optical, morphological and device data. There is an optimum side chain length and contrary to previous observations the MC:PCBM blend layers processed from solution perform better in OPVs than layers processed by thermal deposition under vacuum.