Skillfully deflecting the question: A small amount of piperazine-1,4-diium iodide radically enhances the thermal stability of CsPbI₃ perovskite

Inorganic CsPbI₃ perovskite holds great promise to prepare high-performance and long-term operational perovskite solar cells (PSCs) because of its ideal band gap and intrinsic superb stability. However, due to the low tolerance factor, the photoactive CsPbI₃ perovskite is a high-temperature (330 °C) phase that would spontaneously transit to a non-perovskite phase at ambient temperature. Herein, we incorporate piperazine-1,4-diium iodide (PZDI₂) into CsPbI₃ perovskite to stabilize the photoactive phase. PZD cations are proved to be inserted between layered perovskites to form a Ruddlesden-Popper 2D structure. Excitingly, a small amount of PZDI₂ (3%) radically enhances the thermal stability of the CsPbI₃ perovskite. Specifically, the CsPbI₃·3%PZDI₂ film exhibits no phase transition after heating at 100 °C for 24 h, whereas the pristine CsPbI₃ and MAPbI₃ films are seriously degraded after 16 h and 12 h, respectively. The carbon-based PSCs without the hole transport material (C-PSCs) using the CsPbI₃·3%PZDI₂ film show almost no performance decay after storage in air atmosphere at room temperature for 1200 h and at 85 °C for 200 h, whereas at 85 °C, the pristine CsPbI₃ and MAPbI₃ devices inflict over 20% decay after 40 h and 6 h, respectively.