The effect of polymer solar cell degradation on charge carrier dynamics in benzodithiophene-diketopyrrolopyrrole polymers

Degradation in polymer based organic solar cells still remains poorly understood despite prominent research efforts in recent years. In this work, the impact of photostability and documented morphological evolution of a couple of poly(benzodithiophene-diketopyrrolopyrrole) polymers in their blends with phenyl-C61-butyric acid methyl ester (PCBM) are investigated by a combination of charge extraction techniques. Photo-induced charge carrier extraction by linearly increasing voltage (photo-CELIV) and integral-time of flight (TOF) methods are employed to determine charge carrier mobility and recombination at various stages of photo-degradation in the absence of air. We report the progressive formation of deeper trap states as crucial outcome of photo-degradation within these blends as deduced from our measurements.