Transient charge carrier dynamics in organic solar cell devices studied by simultaneous optical and electric detection.

This article focuses on the development and application of a simultaneous optical and electrical detection (SOED) technique to investigate photogenerated carrier dynamics in practical organic solar cells based on poly(3-hexylthiophene-2,5-diyl) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) bulk heterojunction devices. The SOED method enables concurrent measurement of reflection-mode transient optical absorption (ΔA) and transient photocurrent (Δi), revealing that carrier recombination and transport exhibit power-law decay behaviors characterized by detrapping-limited recombination at times earlier than ~1 μs and trap-free diffusion/drift at later times. Analysis of transit times derived from both ΔA and Δi signals allows calculation of transit mobilities, whose ratio strongly correlates with device photon energy conversion efficiency (PCE), suggesting that charge accumulation at active layer/electrode interfaces delays carrier extraction and reduces efficiency. The study demonstrates that SOED provides detailed insights into carrier dynamics affecting solar cell performance beyond conventional electrical measurements and offers a promising tool for optimizing organic and other thin-film solar devices.