Constructing Robust Top Heterointerface with Quinoid Polymer for High Performance CsPbI₃ Solar Cells

The excellent light absorption and nonvolatilization nature of triiodide cesium lead (CsPbI 3 ) make it a promising candidate for high-performance photovoltaics, but the efficiency of CsPbI 3 photovoltaics is still limited by severe open-circuit voltage ( V OC ) loss caused by nonradiative recombination. Herein, a quinoid polymer (named PAQM-TPD) is used as a dual-functional buffer layer to optimize the interface between the perovskite and the hole transport layer for reducing the V OC loss and broadening the light response in CsPbI 3 perovskite solar cells (PSCs). Introducing PAQM-TPD induces Lewis acid–base interactions with CsPbI 3 to form a stable heterointerface on top of the CsPbI 3 crystal, which can passivate defects and extend the spectral response range. In addition, PAQM-TPD featuring high mobility and matching energy-level alignment generated by the CsPbI 3 /PAQM-TPD heterointerface provides a good driving force for hole transport, reducing the energy loss at the interface. Consequently, the comprehensive interface optimization results in the β-CsPbI 3 PSCs achieving an efficiency of 19.98% and the highest current density (20.98 mA cm –2 ), with a low energy loss of 0.496 eV. Long alkyl side chains in the quinoid polymer also prevent water ingress and stabilize the perovskite heterointerface. Devices treated with PAQM-TPD retained 91% of their initial efficiency after 720 h of storage in an ambient air environment.