Interfacial engineering of dopant-free phthalocyanine hole transporters for >22% efficiency perovskite solar modules

Abstract

The instability of doped Spiro-OMeTAD, a widely used hole transport material (HTM), hinders the industrial progress of n–i–p structured perovskite photovoltaics. Phthalocyanines, known for their stability as HTMs, present a promising alternative for durable devices. However, challenges like energy level mismatches with the perovskite and lower charge mobility have limited their efficiency in small-area devices, affecting high-performance modules. This work addresses these limitations through interfacial engineering between perovskite and phthalocyanine layers, employing alkyl ammonium salts. Post-treatment of the perovskite film with these molecules adjusts the conduction band alignment at the perovskite surface to well match the phthalocyanine energy level. Such a modification also promotes the crystallization of phthalocyanines, improving molecular orientation for enhanced hole transport. Consequently, the optimized solar modules with phthalocyanine-based HTMs without doping achieve a record efficiency of 22.12% (certified 22.05%) for a 12.63 cm² aperture area, almost approaching the performance of Spiro-OMeTAD-based devices. Notably, the unencapsulated device retains over 96% of its initial performance after 2000 hours of continuous 1-sun illumination under maximum power point operating conditions. Furthermore, the encapsulated device maintains its original performance for over 1600 hours under water immersion and heating at 85 °C, simulating more realistic operational conditions.