A Dual-Functional ZSA–CPE Interlayer for Simultaneous Defect Passivation, Energy Alignment, and Stability Enhancement in Inverted Perovskite Solar Cells

Background

Inverted (p–i–n) metal-halide perovskite solar cells (PSCs) are nearing the Shockley–Queisser limit but have their power conversion efficiency (PCE) and operational stability limited by three coexisting loss channels: non-radiative recombination at grain boundaries, energetic misalignment at carrier-selective contacts, and ionic migration under photothermal–humidity stress. Strategies for addressing each of these losses in isolation have produced only slight improvements. APPROACH We present ZSA–CPE, a rationally designed dual-functional interlayer consisting of a zwitterionic self- assembled monolayer (ZSA) with a solution-processed poly(fluorene-alt-benzimidazolium) conjugated polyelectrolyte (CPE), at the perovskite/hole-transport-layer (HTL) interface of MAPbI3-based inverted PSCs. First-principles density functional theory (DFT) calculations supplemented with ultraviolet photoelectron spectroscopy (UPS) guided molecular selection toward simultaneous neutralization of Lewis-acid (Pb2+) and Lewis-base (VI) defects, energy-level matching, and hydrophobic encapsulation.

Results

ZSA–CPE incorporation enhanced (110) crystallographic alignment (Herman parameter f = 0.71 vs. 0.43), reduced root-mean-square surface roughness from 18.4 ± 1.2 nm to 4.7 ± 0.6 nm, suppressed mid-gap trap density 35- fold (Nt: 2.4×1016 → 6.8×1014 cm−3), and lengthened average carrier lifetime 3.7-fold (τavg: 84 ns → 312 ns). Champion devices delivered PCE = 26.1 ± 0.4 %, Voc = 1.21 V, Jsc = 26.4 mA cm−2, FF = 81.8 %, and a near-zero hysteresis index of 0.008, with T90 > 1,200 h under ISOS-L-2 (85 °C / 85 % RH / 1 sun).

Significance

The cooperative integration of complementary passivation and energy-aligning chemistries establishes a transferable design rule for high-efficiency, intrinsically stable PSCs and provides a quantitative blueprint for translating molecular synergy into device-level performance gains across emerging perovskite chemistries.