Tuning the buried interface with d-sorbitol-modified mixed SAMs for high-efficiency inverted perovskite solar cells

Abstract

One of the key bottlenecks limiting high efficiency and long-term stability in perovskite solar cells (PSCs) is non-radiative recombination and slow interfacial-process-related losses at the buried transparent conducting oxide/perovskite interface. Here, a mixed 2PACz/MeO-2PACz self-assembled monolayer (SAM) (1 : 3, w/w) is deposited on high-haze FTO to form a hole-selective contact in an inverted (p–i–n) architecture, and the buried interface is further modified with D-sorbitol (DS), a polyol bearing multiple –OH groups. X-ray diffraction confirms that mixed-SAM formation and DS treatment preserve the perovskite crystal structure without detectable secondary phases, while sharpening diffraction features consistent with more controlled crystallization. The mixed-SAM enables smoother perovskite growth, and DS treatment preserves this smooth morphology while increasing surface wettability. Steady-state photoluminescence increases and time-resolved PL exhibits prolonged decay components after DS treatment, consistent with reduced non-radiative recombination losses associated with the buried interface. Electrochemical impedance spectroscopy shows an increased recombination resistance (R_rec), supporting reduced interfacial recombination. Surface-sensitive characterization further indicates DS-assisted reorganization of the mixed-SAM/FTO contact toward a more uniform and chemically accessible anchoring configuration. Consequently, DS-modified mixed-SAM device increases J_sc from 19.3 to 22.4 mA cm⁻² and V_oc from 1060 to 1080 mV, boosting PCE from 14.1% to 16.1%, while lowering the hysteresis index from 0.032 to 0.022. Additionally, DS-treated devices exhibit improved inert shelf-storage stability, retaining 81.7% of the initial normalized PCE after 8 days, versus 42.2% for reference. Overall, polyol-assisted mixed-SAM engineering provides a simple, solution-processable route to mitigate slow interfacial losses and improve p–i–n PSC performance and stability.