Unraveling the dual functional mechanism of light absorption and hole transport of Cu2CdxZn1-xSnS4 for achieving efficient and stable perovskite solar cells.

Broadening the near-infrared (NIR) spectrum of device is critical to further improve the power conversion efficiency (PCE) of the perovskite solar cells (PSCs). In this work, novel Cu2CdxZn1-xSnS4 (CZTS: Cd) film prepared by thermal evaporation method was employed as the NIR light-harvesting layer to complement absorption of the perovskite. At the same time, Au nanorods (NRs) were introduced into the hole transporting layer (HTL) to boost the utilization of CZTS: Cd to NIR light through localized surface plasmon effect. The perovskite/CZTS: Cd and Au NRs integrated PSCs can extend the photoelectric response until to 900 nm. And more, the well matched energy levels between CZTS: Cd and perovskite can effectively extract holes from perovskite and depress the charge-carrier recombination. As a result, the champion PSC device insulating with CZTS: Cd and Au NRs demonstrates a remarkably increased PCE from 19.30% to 21.11%. The modified PSC devices also demonstrate highly improved long time stability. The device retains the PCE of 87% after 500 h even under air with a relative humidity of 85%, implying the superior humidity stability of the devices with CZTS: Cd. This work suggests that perovskite/inorganic integrated structure is a promising strategy to broaden and boost the NIR response of the PSCs.