Ultrathin Hole Extraction Layer for Efficient Inverted Perovskite Solar Cells

Inverted perovskite solar cells (PSCs) incorporating poly­(3,4-ethylenedioxythiophene)–poly­(styrenesulfonate) (PEDOT) as the hole transport/extraction layer have been broadly investigated in recent years. However, most PSCs which incorporate PEDOT as the hole transport layer (HTL) suffer from lower device performance stemming from reduced photocurrent and low open-circuit voltage around 0.95 V. Here, we report an ultrathin PEDOT layer as the HTL for efficient inverted structure PSCs. The transparency, conductivity, and resulting film morphology were studied and compared with traditional architectures and thicker PEDOT layers. The PSC device incorporating an ultrathin PEDOT layer shows significant improvement in short-circuit current density (<i>J</i><sub>SC</sub>), open-circuit voltage (<i>V</i><sub>OC</sub>), and power conversion efficiency. Because ultrathin PEDOT layers can be easily obtained by dilution, this study suggests a simple way to improve the PSC performance and provide a route to further reduce the fabrication complexity and cost of PSCs.