Key Takeaways & Executive Findings
- •• A vertical interfacial engineering strategy via dual-interface modification (Sn(OTF)2 at NiOx/perovskite, 4-Fluorophenylethylamine chloride (F-PEA) at perovskite/C60) solves energy-level mismatches in two-step-processed (TSP) p-i-n PSCs, boosting PCE to 25.6%. • Sn(OTF)2 enhances NiOx conductivity, suppresses ion migration, and forms a Pb-Sn perovskite interlayer; F-PEA eliminates PbI2, forming a 2D capping layer for defect passivation. • Optimized NiOx-based TSP p-i-n PSCs retain 84% initial power conversion efficiency after 720-h light illumination, providing design principles for 26%-efficiency devices. • The study reveals that residual PbI2 clusters in TSP films cause Schottky heterojunctions and energy-level mismatches, which are effectively mitigated by the dual-interface modification.
Abstract
Two-step-processed (TSP) inverted p-i-n perovskite solar cells (PSCs) have demonstrated significant promise in tandem applications. However, the power conversion efficiency (PCE) of TSP p-i-n PSCs rarely exceeds 24%. Here, we demonstrate that TSP perovskite films exhibit a vertically gradient distribution of residual PbI2 clusters, which form Schottky heterojunctions with the perovskite, leading to substantial interfacial energy-level mismatches within NiOx-based TSP p-i-n PSCs. These limitations were effectively addressed via a vertical interfacial engineering enabled by dual-interface modification incorporating tin trifluoromethanesulfonate (Sn(OTF)2) and 4-Fluorophenylethylamine chloride (F-PEA) at the NiOx/perovskite and perovskite/C60 interfaces, respectively. The functional Sn(OTF)2 not only enhances the conductivity of NiOx films but also suppresses ion migration, while inducing the formation of a Pb-Sn mixed perovskite interlayer that precisely regulates the energy level at the NiOx/perovskite interface. Complementally, F-PEA post-treatment effectively converts surface residual PbI2 clusters into a 2D perovskite capping layer, which simultaneously passivates surface defects and enhances energy-level alignment at the perovskite/C60 interface. Consequently, the optimized NiOx-based TSP p-i-n PSCs achieve a notable PCE of 25.6% with superior operational stability. This study elucidates the underlying mechanisms limiting the efficiency of TSP p-i-n PSCs, while establishing design principles for these devices targeting 26% efficiency.
1. Introduction
Perovskite solar cells (PSCs) have garnered significant global research interest over the past decade owing to their exceptional advantages, including cost-effective fabrication, high device efficiency, and superior defect tolerance [1, 2]. Through innovations in material design and device engineering, the power conversion efficiency (PCE) of PSCs has reached certified record values of 27.0% in single-junction configurations and 34.6% in perovskite-silicon tandem architectures, positioning them as a leading candidate for next-generation photovoltaic technologies [3–5]. Among strategies for advancing PSCs, the inverted p-i-n architecture has attracted considerable attention due to its negligible hysteresis, low-temperature processability, high stability, and low parasitic absorption. Such features render this architecture particularly suitable for flexible devices and monolithic perovskite-silicon tandem solar cells.
Within p-i-n device architectures, perovskite films are typically deposited on a hole transport layer (HTL) such as poly(3,4-ethylenedioxythiophene)/polystyrene sulfonate (PEDOT/PSS) and poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA). However, PEDOT/PSS suffers from inherent hydrolytic and UV-induced degradation, whereas PTAA exhibits poor surface wettability, posing substantial manufacturing challenges [6–8]. In comparison, nickel oxide (NiOx), an inorganic wide-bandgap semiconductor, has emerged as a promising alternative hole transport material (HTM) for perovskite photovoltaics owing to its combination of exceptional stability, efficient charge carrier transport, and low-cost processing [9–11]. Yu et al. developed H2O2-engineered NiOx as the HTM, demonstrating that H2O2 addition enhances NiOx films’ conductivity and generates abundant surface hydroxyl groups for improved surface wettability. This approach yielded NiOx-based p-i-n PSCs with a certified PCE of 25.2% [12].
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Wenhao Zhou, Heng Liu, Haiyan Li, Weihai Zhang, Hui Li, Xia Zhou, Rouxi Chen, Wenjun Zhang, Tingting Shi, Antonio Abate, Hsing-Lin Wang (2026). Vertical Interfacial Engineering in Two-Step-Processed Perovskite Films Enabled by Dual-Interface Modification for High-Efficiency p-i-n Solar Cells. Nano-Micro Letters. https://doi.org/10.1007/s40820-025-02010-w
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Frequently Asked Questions
What is the main achievement of this study?
The study achieves a power conversion efficiency (PCE) of 25.6% in two-step-processed p-i-n perovskite solar cells by employing dual-interface modification with Sn(OTF)2 and F-PEA, addressing energy-level mismatches and enhancing stability.
How does Sn(OTF)2 improve device performance?
Sn(OTF)2 enhances the conductivity of NiOx films, suppresses ion migration, and induces the formation of a Pb-Sn mixed perovskite interlayer that precisely regulates the energy level at the NiOx/perovskite interface.
What role does F-PEA play in the device?
F-PEA post-treatment converts surface residual PbI2 clusters into a 2D perovskite capping layer, which passivates surface defects and enhances energy-level alignment at the perovskite/C60 interface.
What is the operational stability of the optimized devices?
The optimized NiOx-based TSP p-i-n PSCs retain 84% of their initial power conversion efficiency after 720 hours of light illumination, demonstrating superior operational stability.
What are the design principles for achieving 26% efficiency?
The study establishes design principles for TSP p-i-n PSCs targeting 26% efficiency, emphasizing the importance of vertical interfacial engineering to mitigate energy-level mismatches and residual PbI2-induced Schottky barriers.
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