In Situ Surface Sulfidation of CsPbI<sub>3</sub> for Inverted Perovskite Solar Cells
Xuemin Guo, Chunyan Lu, Wenxiao Zhang, Haobo Yuan, Hui Yang, Acan Liu, Zhengbo Cui, Wen J. Li, Yuyang Hu, Xiaodong Li, Junfeng Fang
Abstract
Inverted CsPbI 3 commonly exhibits a more p-type surface than bulk, which induces severe interfacial recombination and, thus, limits the device’s V oc and efficiency in inverted perovskite solar cells (PSCs). Here, a gradual CsPbI 3 /PbS heterojunction is constructed to inhibit such recombination through in situ chemical sulfidation with N, N ′-diphenylthiourea (DPhTA). DPhTA can directly react with CsPbI 3 to form PbS and induce a p- to n-type transition at the CsPbI 3 surface, which leads to the energy level bending downward and establishing a gradual CsPbI 3 /PbS heterojunction at the top of the surface region. PSCs with DPhTA exhibit a high V oc of 1.20 V and reach over 20% efficiency (stabilized efficiency of 19.5%), which is among the highest efficiencies of inverted CsPbI 3 PSCs. In addition, the strong Pb–S bond and well-matched crystal lattice of PbS will protect and stabilize the CsPbI 3 layer beneath, thereby greatly improving the device’s stability. Resulting PSCs retain over 95% of the initial efficiency whether after maximum power point (MPP) tracking for 1200 h or N 2 storage for 300 days.