Temperature Dependence of Charge Carrier Generation in Organic Photovoltaics

The charge generation mechanism in organic photovoltaics is a fundamental yet heavily debated issue. All the generated charges recombine at the open-circuit voltage (${V}_{\mathrm{OC}}$), so that investigation of recombined charges at ${V}_{\mathrm{OC}}$ provides a unique approach to understanding charge generation. At low temperatures, we observe a decrease of ${V}_{\mathrm{OC}}$, which is attributed to reduced charge separation. Comparison between benchmark polymer:fullerene and polymer:polymer blends highlights the critical role of charge delocalization in charge separation and emphasizes the importance of entropy in charge generation.