Ultra-thin ZnO film as an electron transport layer for realizing the high efficiency of organic solar cells

Abstract

To overcome the limits of low charge transport efficiency and high absorption in the UV region of conventional thick ZnO layers in organic solar cells, herein we introduce an ultra-thin ZnO film (4 nm) into PBDTTT-CF:PC₇₀BM bulk heterojunction organic solar cells, as the electron transport layer, and realize a power conversion efficiency of 7.51%, which is dramatically higher than that of a device using general ZnO film (28.1 nm). Various techniques from both steady-state and ultra-fast views reveal that the devices with an ultra-thin ZnO film (less than 10 nm) show a higher built-in potential compared to the device with a 28.1 nm ZnO film. Such an enhancement of the built-in potential could facilitate the photo-generated excitons dissociating into free charge carriers and benefit the transport of charge carriers to the electrode. Thus, we have supplied an efficient electron conducting layer not only for the photovoltaic community but also for other photoelectronic devices.