Octamethyl-substituted Pd(II) phthalocyanine with long carrier lifetime as a dopant-free hole selective material for performance enhancement of perovskite solar cells

Recently, perovskite solar cells (PSCs) have emerged as the most promising photovoltaic devices owing to their rapidly increased power conversion efficiency (PCE). Small molecule metallophthalocyanine compounds, as thermally and chemically stable materials with high hole mobilities, are considered to be potential candidates for stable hole-selective layers (HSLs) in PSCs. In this study, a novel metallophthalocyanine derivative with a heavy palladium (Pd) atom and octamethyl substituents (PdMe2Pc) was designed and synthesized. The introduction of the heavy Pd atom endows the material with a long carrier lifetime, and without dramatically reducing its mobility. As a result, PdMe2Pc exhibits a long diffusion length (26.00 nm), which is beneficial for restraining charge recombination. Planar PSCs that employed PdMe2Pc as a HSL displayed a high PCE of 16.28% and good long-term stability. This result indicates that PdMe2Pc could be a promising HSL for PSCs with high efficiencies and high stabilities.