Breaking the space charge limit in organic solar cells by a novel plasmonic-electrical concept

As a fundamental electrostatic limit, space charge limit (SCL) for photocurrent is a universal phenomenon and of paramount importance for organic semiconductors with unbalanced photocarriers mobility and high exciton generation. Here we proposed a new plasmonic-electrical concept to manipulate electrical properties of organic devices including photocarriers recombination, transport and collection. As a proof-of-concept, organic solar cells (OSCs) comprising metallic planar and grating electrodes are systematically investigated with 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. The particular reason is that plasmonically induced photocarriers redistribution shortens the transport path of low-mobility holes, which are collected by the grating anode. The work demonstrated and explained the SCL breaking with the plasmonic-electrical effect. Most importantly, the plasmonic-electrical concept will open up a new way to manipulate both optical and electrical properties of semiconductor devices simultaneously.