Berlin 2012 – scientific programme
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 31: Organic semiconductors II
CPP 31.2: Talk
Thursday, March 29, 2012, 10:00–10:15, C 130
Doping as a new approach in promoting charge separation in polymer:fullerene solar cells — •Daniel Riedel1, Felix Deschler1, Enrico Da Como1, Jochen Feldmann1, Bernhard Ecker2, and Elizabeth von Hauff2 — 1PhOG, Department of Physics, LMU, Munich — 2Institute of Physics, University of Freiburg
Charge separation at polymer:fullerene interfaces is the primary process for organic bulk-heterojunction solar cells. Following the ultrafast photoinduced charge transfer, electrons and holes are still bound because of Coulomb interactions, resulting in the formation of charge transfer excitons (CTEs). Those are known to play a crucial role in solar cells being responsible for the open circuit voltage and the short circuit current. In this contribution, we propose a novel strategy to overcome some of the recombination channels due to charge transfer excitons. This new approach considers the modification of the electronic properties of the conjugated polymer by doping with F4TCNQ molecules. The free holes induced by F4TCNQ on the low-bandgap polymer PCPDTBT fill the tail of states in the highest occupied molecular orbital (HOMO) and in addition are expected to screen Coulomb interactions of CTEs at the interface between PCPDTBT and the fullerene derivative PCBM. By the unique combination of time resolved photoluminescence and photoinduced absorption spectroscopy, we demonstrate how doping results in a decreased population of CTEs and enhanced formation of free carriers. The spectroscopy experiments are complemented by measurements on solar cells showing an overall increase of more than 30% in the power conversion efficiency.