Extracting charge carrier mobility in organic solar cells through space-charge-limited current measurements

Abstract

Mobility is a critical parameter influencing the overall performance of organic solar cells (OSCs). Herein, we innovatively elucidated the intricate interrelation between the photovoltaic molecular structures and the methodologies employed for the extraction of charge carrier mobility in OSCs. We proposed a simple yet effective principle to accurately extract charge carrier mobility values using the standard space-charge-limited current (SCLC) measurement, while critically assessing theoretical and experimental deficiencies through the drift-diffusion analysis. It was found that field-dependent charge transport is necessitated to describe the prominent long-range intrachain hopping carrier behavior in polymers, while short-range intermolecular hopping results in trap-involved charge transport within small molecular acceptors. Based on the above understanding, a synergetic inter/intra-molecular hopping strategy was proposed to fabricate thick-film all-polymer OSCs, and an unprecedented power conversion efficiency (PCE) of 16.61 % was achieved in the 300 nm PM6:PY-IT OSC. This work not only presents a precise and straightforward approach for measuring mobility values, but also provides a significant reference about charge carrier transport to make optimal decisions regarding photovoltaic material design and device fabrication process of high-performance OSCs.