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Although C₆₀is usually the electron transport layer (ETL) in inverted perovskite solar cells, its molecular nature of C₆₀leads to weak interfaces that lead to non-ideal interfacial electronic and mechanical degradation. Here, we synthesized an ionic salt from C₆₀, 4-(1',5′-dihydro-1'-methyl-2'H-[5,6] fullereno-C₆₀-I_h-[1,9-c]pyrrol-2'-yl) phenylmethanaminium chloride (CPMAC), and used it as the electron shuttle in inverted PSCs. The CH₂-NH₃⁺head group in the CPMA cation improved the ETL interface and the ionic nature enhanced the packing, leading to ~3-fold increase in the interfacial toughness compared to C₆₀. Using CPMAC, we obtained ~26% power conversion efficiencies (PCEs) with ~2% degradation after 2,100 hours of 1-sun operation at 65°C. For minimodules (four subcells, 6 centimeters square), we achieved the PCE of ~23% with <9% degradation after 2,200 hours of operation at 55°C. 

The enargite phase of Cu3AsS4 (ENG) is an emerging photovoltaic material with a ∼1.4 eV bandgap and is composed of earth abundant elements with favorable defect properties arising from the differing ionic radii of the constituent elements. Unfortunately, ENG-based photovoltaic devices have experimentally been shown to have low power conversion efficiencies, possibly due to defects in the material. In this joint computational and experimental study, we explore the defect properties of ENG and employ synthesis approaches, such as silver alloying, to reduce the density of harmful defects. We show that shallow copper vacancies (VCu) are expected to be the primary defects in ENG and contribute to its p-type character. However, as shown through photoluminescence (PL) measurements of synthesized ENG, a large mid-bandgap PL peak is present at ∼0.87 eV from a band edge, potentially caused by a copper- or sulfur-related defect. To improve the properties of ENG films and mitigate the mid-bandgap PL, we employed an amine-thiol molecular precursor-based synthesis approach and utilized silver alloying of ENG films. While silver alloying did not affect the mid-bandgap PL peak, it increased grain size and lowered film porosity, improving device performance. In conclusion, we found that incorporating silver such that [Ag]/([Ag] + [Cu]) is 0.05 in the film using an amine-thiol based molecular precursor route with As2S3 as the arsenic source resulted in improved photovoltaic device performance with a champion device of efficiency 0.60%, the highest reported efficiency for an Cu3AsS4 (ENG)-based device to date. 

A phosphorus-containing Lewis-base molecule passivates and bridges perovskite grain boundaries and interfaces.