Static and Dynamic Disorder of Charge Transfer States Probed by Optical Spectroscopy

Since the key role of charge transfers (CT) states has been identified for organic solar cells (OSCs), research into their properties is a timely topic. Conventionally, absorption and emission spectra are described in terms Marcus’ electron transfer theory. This single site approach with essential parameter being reorganization energy. Thus, it ignores ensemble effects, notably static disorder that inevitably present spin-coated OSC film. Here time dependent photoluminescence spectroscopy applied on blends polymeric donor MeLPPP either non-fullerene acceptor SF-PDI2 or PC61BM within temperature range from 295 to 5 K. The authors monitor how initially excited singlet converted emissive CT states. Concomitantly, residual singlets observed rather than hybrid CT-states. spectral diffusion this process discussed. From linewidths absorption, fluorescence, emission, dynamic contributions total inferred. In both blends, at K, contribution comparable disorder.