Self-Assembled π-Conjugated Hole-Selective Molecules for UV-Resistant High-Efficiency Perovskite Solar Cells

Ultraviolet (UV) light-induced degradation, particularly occurring at the buried interface, has emerged as a significant stability challenge, severely limiting the widespread applications of perovskite solar cells (PSCs). Here, we rationally design and synthesize novel thiophene-modified self-assembled π-conjugated hole-selective molecules, namely (4-(3,6-bis(5-methylthiophen-2-yl)-9H-carbazol-9-yl)phenyl)phosphonic acid (Me-TPCP), affording UV-stable high-efficiency PSCs. Simultaneously incorporating phenyl and thiophene groups enhances molecular conjugation, effectively protecting the fragile bonds between the carbazole core and the phosphonic acid group. This modification results in enhanced intrinsic UV stability and improved hole transport ability of the molecule. Furthermore, thiophene grafted on the carbazole coordinates with the Pb²⁺ ions in perovskite, enhancing the binding of perovskite to hole-selective molecules. Consequently, the crystallinity of the perovskite film is significantly improved, along with decreased defect density, thereby inhibiting its degradation under UV light illumination. By introducing methyl groups, the molecular stability is further enhanced, and the energy level of Me-TPCP is finely tuned, resulting in a lower interfacial energy barrier that facilitates more efficient hole extraction. With these advantages, inverted PSC devices based on Me-TPCP achieve a significantly higher efficiency of 25.62% than the control devices (23.85%). Meanwhile, these devices demonstrate a remarkable enhancement in UV stability, as well as improved operational and thermal stability.