Efficiency enhancement in inverted planar perovskite solar cells by synergetic effect of sulfated graphene oxide (sGO) and PEDOT:PSS as hole transporting layer

Inverted planar perovskite solar cells (PSCs) exhibiting a high power conversion efficiency (PCE) have mainly been demonstrated by using poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as the hole transport layer (HTL). As an alternative to the PEDOT:PSS, graphene oxide (GO) is also employed as a HTL in PSCs with decent PCEs. However, the strong acidity and hygroscopicity of PEDOT:PSS and insulting property of GO were the major factors for hindering the fabrication of high-performance PSCs. Here, we demonstrated sulfated graphene oxide (sGO) as a HTL replacing the conventionally used GO and PEDOT:PSS in PSCs, but pristine sGO as simple HTL cannot improve photovoltaic performance of PSCs with a maximum efficiency of 9.9%. Hence, we report a simple solution route for preparing a sGO–PEDOT:PSS composite HTL by combining solution-processable sGO with commercialized PEDOT:PSS solution. The PSC fabricated with 1 : 1 sGO–PEDOT:PSS HTL shows a dramatically enhanced PCE of 13.9%, versus 11.5% for PSC with pristine PEDOT:PSS HTL. This promising strategy could be a critical step toward the ideal HTL design for the advancement of practical perovskite solar cells.