Dissolution-Tailored Electrodeposition of High-Mobility Cu2O Transport Layers Beyond Conventional Methods

Perovskite solar cells (PSCs) require hole transport materials (HTMs) with high carrier mobility, structural stability, and superior film quality. Cuprous oxide (Cu₂O), an inorganic p-type semiconductor with a 2.17-eV direct bandgap and intrinsic vacancies, is a promising alternative to unstable organic HTMs. Herein, bidirectional pulsed (BP) electrodeposition is employed to overcome limitations of conventional direct current (DC) methods, which accumulate Cu²⁺ impurities, disordered grains, and high surface roughness due to unidirectional deposition. By introducing periodic dissolution phases and precisely regulating forward/reverse voltages (-0.4 V deposition; 0.03 V dissolution), a dynamic deposition-dissolution-redeposition equilibrium is achieved. This process selectively eliminates high-energy crystal facets/defects while promoting (100)-oriented growth, yielding films with significantly enhanced phase purity (77.38% Cu⁺ vs. 55.89% for DC) and atomically smooth surfaces (Ra < 5.00 nm). Optimized BP-Cu₂O films exhibit superior optoelectronic properties: carrier mobility (46.14 vs. 42.12 cm²/V·s), carrier density (9.06 vs. 8.09 × 10²¹ cm^-3), 10% lower resistivity (1.62 vs. 1.73 × 10^-5 Ω/cm), and 92% visible-light transmittance. This work establishes BP electrodeposition as a single-step, post-processing-free strategy for high-performance Cu₂O HTLs, providing a viable pathway toward efficient and stable PSCs.