Efficient carrier transport via dual-function interfacial engineering using cesium iodide for high-performance perovskite solar cells based on NiO_X hole transporting materials

As a famous hole transporting material, nickle oxide (NiO_X) has drawn enormous attention due to its low cost and superior stability. However, the relatively low conductivity and high-density surface trap states of NiO_X severely limit device performance in solar cell applications. Interfacial engineering is an efficient approach to achieve remarkable hole-transporting performance by surface passivation. Herein, the efficient NiO_X hole transport layer was prepared by surface passivation engineering strategy via facile solution processes with cesium iodide (CsI). It is demonstrated that CsI plays a super-effective dual-function role in inverted solar cell device: On one hand, the presence of CsI hugely passivates the surface trap states at the NiO_X/perovskite interface along with obviously improved conductivity by the incorporated Cs⁺; on the other hand, the ions immigration is significantly suppressed by the presence of I ion for high-quality perovskite films, resulting in a stable contact interface. The ameliorative interface leads to largely reduced carrier non-radiative recombination, attributing to boosted carrier extraction efficiency. As a result, decent power conversion efficiency (PCE) of 18.48% with a noticeable fill factor (FF) beyond 80% was achieved. This facile and efficient surface engineering approach with dual-function shows excellent potential for the design of high-performance functional interfacial modification layer to achieve high-performance solar cells.