Interface modification of imidazolium ionic liquid toward efficient and stable carbon-electroded CsPbI2Br perovskite solar cells

The hole-transport-layer-free (HTL-free) carbon-electrode CsPbI₂Br perovskite solar cells (PSCs) have garnered significant interest due to their process compatibility and excellent stability. Nevertheless, surface and grain boundary defects in perovskite films inevitably serve as non-radiative recombination sites, critically limiting device performance. Herein, an interface engineering strategy employing 1-benzyl-3-methylimidazolium chloride is proposed to restructure the perovskite/carbon interface in HTL-free architectures. The results demonstrated that the ionic liquid effectively passivate the defects on the surface of the perovskite film, associated with reduced defects, enhanced carrier transport, and induced hydrophobicity properties, thereby improving the overall performance of the perovskite solar cells. The modified carbon-based perovskite solar cell device, in the absence of a hole transport layer, exhibits a champion PCE of 13.96 %, with V_OC of 1.25 V, J_SC of 14.88 mA cm⁻², and FF of 75 %. Moreover, the unencapsulated 1-3-MIMCl-modified device retained 84.7 % of its initial efficiency after 1200 h in a glove box, demonstrating superior long-term stability compared to the control device.