Researchers from Hebei University of Technology, Hohai University, University of Chinese Academy of Sciences, ChangZhou S.C Exact Equipment Co., The Hong Kong Polytechnic University and Kunming University of Science and Technology have developed a dual-molecule interfacial strategy that addresses key loss mechanisms in inverted perovskite solar cells (PSCs), achieving certified efficiencies above 27% alongside strong operational stability and scalability.
In inverted (p–i–n) PSC architectures, performance is often limited by interfacial recombination and chemical instability at the NiOx/perovskite junction. In particular, Ni³⁺-triggered redox reactions and a high density of buried-interface defects lead to nonradiative losses and long-term degradation. While phosphonic acid self-assembled monolayers (SAMs) such as Me-4PACz are widely used to improve hole extraction and suppress interfacial reactions, their defect passivation capability remains limited, especially across diverse defect types at buried interfaces. To overcome these constraints, the researchers introduced 9H-carbazol-2-yl trifluoromethanesulfonate (CzOTf) as a cooperative modifier, coassembling it with Me-4PACz to form an interface-locked dual-molecule contact at the NiOx/perovskite interface. Rather than replacing the existing SAM, CzOTf integrates into the molecular layer, creating a mixed-SAM system with complementary functionalities.
The mechanism relies on two synergistic interaction channels. First, π–π–stabilized cofacial packing between the carbazole cores of Me-4PACz and CzOTf rigidifies molecular orientation and enhances interfacial electronic coupling, enabling more efficient hole extraction. Second, the sulfonate group in CzOTf introduces multidentate coordination with Pb-related defects, expanding passivation coverage while simultaneously alleviating interfacial tensile stress during perovskite crystallization. This combined effect improves buried-interface morphology, suppresses nonradiative recombination, and stabilizes interfacial chemistry.
Morphological analysis supports these effects. “As shown by the scanning electron microscopy (SEM), the Me-4PACz–based control perovskite exhibits pervasive pinhole defects and discontinuities at the bottom interface,” the research team explained. “In contrast, the CzOTf-modulated film forms a substantially denser, more compact, and pinhole-suppressed interfacial layer.” They further noted: “CzOTf not only densifies the buried interface but also facilitates perovskite crystallization on top of the modulated contact, in agreement with the SEM observations and confirming its beneficial role in buried-interface engineering,” and added that “CzOTf modulation in the Me-4PACz sample induces a less negative slope, unambiguously confirming that CzOTf incorporation promotes tensile-stress release in the perovskite film.”
The devices were fabricated in a standard inverted structure consisting of an FTO substrate, a NiOx hole transport layer modified with the Me-4PACz+CzOTf mixed SAM, a perovskite absorber, a C60 electron transport layer, a bathocuproine (BCP) buffer, and a thermally evaporated Ag electrode.
Under standard test conditions, the optimized cell achieved a power conversion efficiency of 27.3%, with an open-circuit voltage of 1.185 V, a short-circuit current density of 26.30 mA cm², and a fill factor of 87.64%. A reference device without CzOTf delivered 26.20% efficiency, 1.172 V VOC, 26.05 mA cm² JSC, and an 85.79% fill factor, highlighting simultaneous improvements in voltage, current, and fill factor due to reduced interfacial losses.
The approach is compatible with vacuum flash evaporation and extends to wider applications. Certified efficiency reached 27.31% (champion 27.32%) for 1.53 eV single-junction devices, while integration into perovskite/silicon heterojunction (HJT-Si) tandems yielded an efficiency of 32.84%.
Importantly, the interfacial design also translates to large-area modules. A 766 cm² device achieved a power conversion efficiency of 21.54%, with a 50.93 V open-circuit voltage, 0.4040 A short-circuit current, and an 80.20% fill factor, demonstrating scalable film quality and uniform charge extraction.
Operational stability is significantly improved. “The CzOTf-modulated perovskite solar cerlls retain 92% of their initial efficiency after 2000 hours of continuous light soaking,” the scientists stated. “The CzOTf-modulated large-area module operated stably outdoors for 35 days without degradation.”
By simultaneously addressing interfacial redox reactions, defect passivation, and stress management within a single molecular framework, this dual-molecule strategy provides a generalizable route toward high-efficiency, low-loss, and scalable inverted perovskite photovoltaics.
