Exploring temperature effects on bulk heterojunction organic solar cell parameters from the analysis of a second-order recombination model

The performance of organic thin-film solar cells is determined by a series of factors arising from the electrical and optoelectronic properties of each layer that composes the devices. However, a correct theoretical analysis of electronic transport, from the generation and recombination of photocarriers to their extraction by the electrodes, is of paramount importance in the race for more efficient solar cells, becoming a beacon in understanding all the electrodynamic phenomena involved, pointing the corrections that must be made to the devices. In this work, we make comparison between two classics bulk heterojunction organic solar cells, having PCDTBT or PTB7-Th as electron donor molecules and the fullerene PC₇₁BM as acceptor. Experimental current-voltage results of the two devices, carried out at different temperatures, were compared from the perspective of a recently developed theoretical expression, and the filling factor was analyzed as a function of the merit factor θ_o, which is directly related to the ratio between the recombination rate and extraction rate of the photocarriers. We also applied that fill factor analysis to the best solar cells based on non-fullerene acceptors.