Inverted (p-i-n) perovskite solar cells (PSCs) employing carbon-based electrodes offer a promising pathway toward scalable, low-cost, and operationally stable photovoltaics; however, their performance is frequently constrained by interfacial losses at the electron-selective contact. Here, we report high-efficiency for such devices, enabled by an engineered PCBM/SnOₓ interface combined with carbon electrode lamination, fully compatible with low-temperature and vacuum-free top-contact processing. A thin interlayer of ethoxylated polyethylenimine (PEIE) is introduced on top of PCBM as a permanent interfacial dipole, facilitating uniform SnOₓ nucleation during atomic layer deposition (ALD) and enhancing charge extraction at the perovskite/ETL interface.

A systematic comparison of different ALD SnOₓ processes reveals that devices fabricated without PEIE exhibit pronounced S-shaped current–voltage characteristics and limited fill factors, indicative of non-ideal interfacial energetics and injection barriers. Incorporation of PEIE effectively suppresses this, resulting in improved charge carrier extraction, reduced interfacial recombination, and enhanced electron selectivity. Under simulated AM 1.5G illumination (1 sun), optimized devices achieve power conversion efficiencies (PCE) exceeding 20.5%, with high open-circuit voltages and fill factors reproducibly maintained across multiple fabricated cell batches. This performance approaches that of silver-based reference devices (PCE ≈ 22%), where the remaining efficiency difference is primarily attributed to a higher short-circuit current density due to enhanced reflection by the silver layer rather than inferior interfacial quality in the carbon-based architecture.

Notably, the same device design exhibits excellent performance under low-light conditions relevant for indoor photovoltaics. At an illumination level of 500 lux, the power conversion efficiency reaches 32.4%, accompanied by negligible shunt leakage. In contrast, the PSC reference employing a metal electrode achieves a PCE of only 27.8%, primarily due to pronounced losses in open-circuit voltage (V_OC) and fill factor (FF). The enhanced fill factor of CPSC under low-light operation is directly linked to the PEIE/ALD SnO_X combination, which improves the ETL layer uniformity, lowers the effective electron extraction barrier and suppresses space-charge-limited transport at reduced carrier densities, thereby stabilizing diode behavior under weak illumination. The combination of dipole-assisted interfacial engineering, ALD-compatible processing, and laminated carbon electrodes establishes a robust strategy for high-performance, low-light-optimized carbon-based p-i-n perovskite solar cells.