GUO Zhangwang ^{1, 2, 3, 4}, JIANG Yang ², ZENG Tao ^{1, 3, 4}, CHEN Yunxia ^{3, 4}

(1. School of Energy Science and Engineering, Jingdezhen Ceramic University, Jingdezhen 333403, Jiangxi, China; 2. Foshan Xianhu Laboratory, Foshan 528200, Guangdong, China; 3. National Engineering Research Center for Domestic & Building Ceramics, Jingdezhen Ceramic University, Jingdezhen 333403, Jiangxi, China; 4. Jiangxi Key Laboratory of Advanced Ceramic Materials, Jingdezhen Ceramic University, Jingdezhen 333403, Jiangxi, China)

Extended abstract:

[Background and purposes] In inverted (p-i-n) halide perovskite solar cells (PSCs), improvements in open-circuit voltage, fill factor and long-term stability remain constrained by material and interfacial challenges. Grain-boundary residual PbI₂, undercoordinated Pb²⁺ sites, and related halide-lattice disorder introduce deep-level traps and shunting pathways that increase nonradiative recombination, hinder charge extraction and accelerate performance degradation under operating conditions. To address these problems, we introduce multifunctional hydrochloride salt additive 4‑hydrazinopyridine hydrochloride (4HPCl) into the perovskite precursor. The additive concurrently modulates crystallization kinetics and chemically passivates grain-boundary and surface defects (for example, residual PbI₂ and undercoordinated Pb/halide sites), thereby suppressing nonradiative recombination and improving interfacial charge transport. This strategy yields both high power conversion efficiency and markedly enhanced stability, providing an effective route to fabricate high-performance reliable inverted-structure perovskite solar cells.

[Methods] Inverted PSCs with the stack glass/ITO/NiO_x/Ph-4PACz/perovskite/PEAI/C₆₀/BCP/Ag were prepared using mixed-cation perovskite films (Cs_0.05MA_0.10FA_0.85PbI₃) deposited from a precursor containing MACl and excess PbI₂. The additive 4HPCl was introduced at 0–1 mg·mL^–1, with 0.5 mg·mL^–1 yielding the optimized device performance. Film crystallinity and morphology were characterized by using XRD and SEM. Chemical states and interaction mechanisms were probed by using XPS. Optoelectronic properties were measured by using UV-vis absorption, steady-state and time-resolved photoluminescence (PL/TRPL), PLQY and 2D PL mapping. To quantify the reductions in loss channels, we measured dark J-V leakage, performed space-charge-limited current (SCLC) measurements on electron-only devices to extract defect density, conducted electrochemical impedance spectroscopy (EIS) to obtain recombination resistance and carried out Mott-Schottky analysis to determine the built-in potential. All devices were tested under standard AM 1.5G illumination (100 mW·cm^–2).

[Results] The introduction of 4HPCl produces concurrent and substantial improvements in film quality, optoelectronic properties and device performance. The optimized device attains a champion power conversion efficiency (PCE) of 25.31% (vs. 22.38% for the control) and a notable fill factor of 83.40%, together with enhanced open-circuit voltage and short-circuit current density. These gains arise from multifaceted enhancements of the perovskite film. XRD and SEM analyses results show that 4HPCl reduces residual PbI₂ and enlarges grain size. These morphological improvements suppress non-radiative recombination. The steady-state photoluminescence (PL) intensity increases markedly, the average carrier lifetime rises from 403.77 ns to 1.06 μs and the PL quantum yield is improved by more than twofold. Spatial heterogeneity is also diminished, as demonstrated by the uniform 2D PL mapping. XPS measurements confirm effective multi-site passivation, with consistent shifts in the core-level peaks of I, N and Pb, indicating modified electronic structure through coordination and/or electrostatic interactions. Leakage current and defect density (from 4.68×10¹⁵ to 3.02×10¹⁵ cm^–3) decrease substantially, while recombination resistance and built-in potential increase. As a result, the treated devices show markedly improved thermal aging stability, retaining ~90% of initial PCE after 900 h at 65 ℃.

[Conclusions] A synergistic approach has been developed to improve film quality in inverted perovskite solar cells, by adding multifunctional hydrochloride 4HPCl. The 4HPCl chemically passivates halide vacancies and undercoordinated Pb²⁺ defects at grain boundaries and surfaces. These combined effects strongly suppress nonradiative recombination. The optimized devices reach an open-circuit voltage of 1.166 V and a fill factor of 83.40%, delivering a champion power conversion efficiency of 25.31%. Electrical characterization result shows a marked decrease in leakage current and defect density and improved interfacial charge transport. Moreover, the 4HPCl-treated devices retain about 90% of their initial efficiency after 900 h thermal aging at 65 ℃, demonstrating enhanced stability. The multidimensional defect-passivation strategy revealed in this work provides a clear materials-design principle for producing high-performance stable perovskite optoelectronic devices.

Key words: perovskite solar cells; additive engineering; defect passivation; power conversion efficiency; stability