Toward Better Efficiency of Air-Stable Polyazomethine-Based Organic Solar Cells Using Time-Resolved Photoluminescence and Light-Induced Electron Spin Resonance as Verification Methods

Abstract

Photoinduced charge transfer is a crucial process in the operation of organic solar cells. In this work we used two spectroscopic techniques, namely, time-resolved photoluminescence and light-induced electron spin resonance, which directly detect this phenomenon in blends composed of [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) and two air-stable polyazomethines with different chemical structures, one with thiophene ring and cardo moieties (25Th-cardo) and one with three thiophene rings (2252Th-DMB). For both polymers we observed a photoluminescence with a maximum around 2 eV. In a mixture with PCBM, the photoluminescence of both polymers was quenched. At the same time, the photoluminescence of PCBM was enhanced in a mixture with 25Th-cardo, whereas it was similar to the photoluminescence of pure PCBM in the mixture with 2252Th-DMB. Moreover, for 2252Th-DMB:PCBM, two overlapping lines of electron spin resonance were detected under illumination, one originating from the positive polaron and another fr...