|Wicklein, A.; Ghosh, S.; Sommer, M.; Würthner, F.; Thelakkat, M.: Self-Assembly of Semiconductor Organogelator Nanowires for Photoinduced Charge Separation, ACS Nano 3(5), 1107-1114 (2009) -- DOI: 10.1021/nn9001165|
We investigated an innovative concept of general validity based on an organogel/polymer system to generate donor−acceptor nanostructures suitable for charge generation and charge transport. An electron conducting (acceptor) perylene bisimide organogelator forms nanowires in suitable solvents during gelation process. This phenomenon was utilized for its self-assembly in an amorphous hole conducting (donor) polymer matrix to realize an interpenetrating donor−acceptor interface with inherent morphological stability. The self-assembly and interface generation were carried out either stepwise or in a single-step. Morphology of the donor−acceptor network in thin films obtained via both routes were studied by a combination of scanning electron microscopy and atomic force microscopy. Additionally, photoinduced charge separation and charge transport in these systems were tested in organic solar cells. Fabrication steps of multilayer organogel/polymer photovoltaic devices were optimized with respect to morphology and surface roughness by introducing additional smoothening layers and charge injection/blocking layers. An inverted cell geometry was used here in which electrons are collected at the bottom electrode and holes at the top electrode. The simultaneous preparation of the interface exhibits almost 3-fold improvement in device characteristics compared to the successive method. The device characteristics under AM1.5 spectral conditions and 100 mW/cm2 for the simultaneous preparation route are short circuit current Jsc = 0.28 mAcm−2, open circuit voltage VOC = 390 mV, fill factor FF = 38%, and a power conversion efficiency η = 0.041%.