Quasi-steady-state measurement of exciton diffusion lengths in organic semiconductors

Exciton diffusion plays a decisive role in determining the recent rise in charge-generation yield (CGY) and power-conversion efficiency brought about by non-fullerene acceptor (NFA) solar cells. In this presentation a technique, named pulsed-PLQY, is introduced to measure the exciton diffusion length in organic semiconductors through exciton-exciton annihilation (EEA) without the need for temporal measurements. Pulsed-PLQY is validated by comparing to established EEA techniques using both simulated and experimental results. It is found that Pulsed-PLQY conserves the validity of established EEA techniques while the implementation is faster, easier, significantly simplifies the equipment required, and is less sensitive to experimental conditions than traditional EEA techniques. Utilising pulsed-PLQY, it is found that NFA's have increased diffusion lengths, compared to fullerene acceptors, and that this increase is driven by increases in diffusivity.