Interface engineering with a malononitrile-anchored self-assembled molecule for high-performance carbon-perovskite solar cells

Developing efficient and stable dopant-free hole-transporting materials (HTMs) is essential for low-cost and scalable perovskite solar cells (PSCs), particularly in carbon-electrode architectures. Here, we report HTM-1-SAM, a cyano-functionalized self-assembled molecular layer incorporating an azobenzene π-conjugated framework and a malononitrile-derived dicyano anchoring unit, for n–i–p carbon-based PSCs. X-ray photoelectron spectroscopy and first-principles calculations support coordination of the cyano groups with undercoordinated Pb2+ sites, while atomic force microscopy, photoluminescence/time-resolved photoluminescence, and impedance measurements indicate a smoother interface, efficient interfacial charge transfer, and suppressed recombination. Devices with the FTO/TiO2/MAPbI3/HTM-1-SAM/carbon architecture reach a forward-scan power conversion efficiency (PCE) of 20.38% (Voc = 1.19 V, Jsc = 22.88 mA cm−2, FF = 74.82%) and 20.95% in reverse scan, compared with 18.99% and 19.63%, respectively, for spiro-OMeTAD references. Across 20 devices, HTM-1-SAM delivers a mean PCE of 19.57 ± 0.95%, together with lower hysteresis and a higher recombination resistance. Under 600 h of MPP-tracked illumination in ambient air, the devices retain 77% of their initial PCE; under combined aging at 80 °C and 65% RH, they retain 70%, compared with 36% and approximately 35% for the corresponding spiro-OMeTAD controls. The two-step Cu-catalyzed synthesis also reduces the estimated material cost by more than 13-fold. These results support a direct relationship between molecular design, interfacial passivation, and device performance, and identify HTM-1-SAM as a promising low-cost contact for carbon-electrode PSCs with improved stability.