Mechanistic iron(III) doping of solution-processed MoOx enables universal, stable, and efficient hole transport in organic and perovskite solar cells

Achieving both high efficiency and long-term stability remains a key challenge for organic and perovskite solar cells (OSCs/PSCs), hindered by defects and suboptimal electronic properties in solution-processed transition metal oxide hole transport layers (HTLs). Here, we present a universal valence-engineering strategy for Mo-based HTLs via Fe 3+ doping in ammonium tetramolybdate hydrolysis solutions and low-temperature annealing. Fe incorporation modulates oxygen vacancies and the Mo 6+ /Mo 5+ ratio, yielding Fe-doped molybdenum oxide (FMo) HTLs with improved conductivity, higher work function, and reduced trap density. Devices employing FMo HTLs exhibit superior power conversion efficiencies of 20.50% (OSC) and 26.05% (PSC), along with exceptional stability, outperforming conventional solution-processed and vacuum-deposited counterparts. The strategy is compatible with various active layer systems and is scalable to large-area devices, highlighting its potential for industrial photovoltaic manufacturing.