A new concept to break the space charge limit of organic semiconductors for photovoltaic applications

As a fundamental electrostatic limit, the space charge limit (SCL) for photocurrent is a universal feature and of paramount importance in organic semiconductors with unbalanced electron/hole mobility and high exciton generation. Here, we propose a new concept of plasmonic-electrical effect to manipulate the electrical properties (photocarrier generation, recombination, transport, and collection) of semiconductor devices with the help of plasmonically induced light redistribution. As a proof-of-concept, organic solar cells (OSCs) incorporating metallic planar and grating anodes are systematically investigated for normal and inverted device structures. Interestingly, although strong plasmonic resonances induce abnormally dense photocarriers around a grating anode, the grating-inverted OSC is exempt from space charge accumulation (limit) and degradation of electrical properties in contrast to the planar-inverted and planar-normal ones. It is because abnormally redistributed holes by the plasmonic-electrical effect, despite of the typically low mobility of holes, shorten hopping path of low mobility holes to reach the grating anode. Consequently, the work contributes to the evolution of device architecture to break the SCL with detailed multiphysics explanations. Moreover, the proposed plasmon-electrical concept will open up a novel way to manipulate both optical and electrical properties of organic semiconductor devices for photovoltaic applications.