Effect of the Hole Transporting/Active Layer Interface on the Perovskite Solar Cell Stability

In the field of photovoltaics, perovskite solar cells have attracted great interest due to their high efficiency combined with a strong potential for low cost and good versatility. One of the main issues concerns the intrinsic stability of these cells. To develop mitigation strategies, there is a critical need for a better understanding of the most plausible degradation mechanisms. This work focuses on the impact of the hole transporting layer (HTL) on the stability of planar NIP perovskite solar cells based on MAPbI_3‑xCl_x. From the comparison of two different HTLs (P3HT and PTAA), the crucial role of interfacial materials on the stability of a complete device is demonstrated. Even if PTAA-based devices presented better performances in the initial state, their degradation under mild aging conditions (35 °C, under dark and inert conditions) is more pronounced than that with the P3HT counterpart. Thanks to complementary characterization tools (infrared spectroscopy, X-ray diffraction, UV–visible absorption, and photoluminescence) applied to different stages of the stack assembly (with respectively three, four, or five layers), a degradation mechanism was identified at the perovskite–PTAA interface. These devices consist of several extremely thin layers; the interfaces play an important role on the performances and stability of the complete cells. It is a pioneering work in the community, which could be transposed to other devices and architectures.