Yaohua Mai

Perovskite/Cu(In,Ga)Se ₂ (CIGS) tandem solar cells have emerged as a highly promising thin‐film photovoltaic architecture, combining the exceptional efficiency potential of perovskites with the industrial maturity of CIGS technology. Despite rapid advances in perovskite top cells, overall tandem performance remains fundamentally constrained by the CIGS bottom cell, which critically governs bandgap matching, voltage losses, and interfacial recombination. Here, we provide a comprehensive overview of recent progress in CIGS absorber and interface engineering for tandem applications. We highlight key strategies including Ga‐gradient bandgap engineering, alkali post‐deposition treatment, Ag alloying for low‐temperature growth and bifacial operation, as well as buffer‐layer and intermediate recombination layer optimization. We further discuss how surface morphology and defect chemistry collectively dictate carrier recombination dynamics and interfacial stability in monolithic device architectures. Finally, we outline a roadmap toward the commercialization of perovskite/CIGS tandem photovoltaics. By linking materials‐level engineering with device‐level constraints, this review establishes a unified framework to guide the development of high‐efficiency, scalable, and industrially viable tandem solar technologies.

Surface passivation of perovskite thin‐films via adsorption of amine‐based derivatives plays an important role in minimizing nonradiative recombination. In this work, we developed a novel and efficient amine‐based surface passivation molecule, cystamine dihydrochloride (CH), which possesses a characteristic symmetric structure and exhibits an anomalous passivation mechanism. It is found that the electron‐rich sulfur atoms in central disulfide moiety of CH experience strong short‐range repulsion with surface iodides of perovskites. Consequently, contrary to the conventional attraction‐driven‐based passivation mechanism, the presence of S–I repulsion dictates a unique binding geometry that drives preferential coordination of the two terminal amine groups with undercoordinated Pb ²⁺ while displacing sulfur atoms away from the surface. This repulsion‐induced interfacial reconstruction effectively suppresses the formation of deep‐trap Pb–Pb dimers and thereby significantly suppresses nonradiative recombination. Eventually, the blade‐coated PSCs with CH‐passivated achieve a champion efficiency of 26.15% compared to 23.64% of the control devices, along with markedly improved operational stability. This work provides new insight into repulsion‐mediated interfacial passivation for high‐efficiency and stable perovskite solar cells.

Perovskite photovoltaics are limited by structural instabilities initiated during crystallization and amplified under operation. We report that a lattice-matched Prussian blue scaffold directs heterogeneous nucleation to produce highly oriented, strain-relaxed films. Its redox-active Fe–C≡N–Fe network mediates the conversion of Pb ⁰ and I ⁰ defects, and its rigid open framework suppresses A-site cation redistribution and the resulting electronic inhomogeneity under bias. This strategy yielded champion power conversion efficiencies of 26.1% (n-i-p) and 26.9% (p-i-n; 26.2% certified), scaling to 23.4% in 6-centimeter–by–6-centimeter minimodules and a certified 22.9% in 30-centimeter–by–30-centimeter submodules. Submodules with initial power conversion efficiencies ranging from 20.2 to 21.0% showed robust durability under accelerated aging and no discernible decline relative to a silicon reference over 5 months of outdoor testing.

Antimony selenide (Sb ₂ Se ₃ ) has emerged as a promising photovoltaic absorber owing to its suitable bandgap, high absorption coefficient, and low‐toxicity elemental composition. However, high‐efficiency Sb ₂ Se ₃ solar cells commonly rely on CdS electron‐transport layers, whereas Cd‐free alternatives often suffer from pronounced recombination losses at the Sb ₂ Se ₃ /buffer heterojunction. Herein, we introduce a sub‐nanometer atomic‐layer‐deposited aluminum oxide (Al ₂ O ₃ ) interlayer at the Sb ₂ Se ₃ /Zn _x Sn _1‐x O heterojunction to improve its interfacial electronic quality. Spectroscopic and theoretical analyses indicate that the ultrathin Al ₂ O ₃ induces interfacial chemical interaction and charge redistribution, thereby modifying the local electronic structure and interfacial energetics. Complementary surface and device‐level measurements reveal a more homogeneous near‐surface electronic response, reduced field‐dependent carrier‐collection losses, and mitigated trap‐assisted recombination. Temperature‐dependent V _OC measurements show an increase in the recombination activation energy from 0.910±0.018 to 1.045±0.021 eV, while intensity‐dependent V _OC measurements reveal a decrease in the effective ideality factor from 1.37 to 1.21, consistently indicating a reduced contribution of trap‐assisted recombination, although interface‐related recombination remains an important loss pathway. Consequently, the optimized Sb ₂ Se ₃ /Al ₂ O ₃ /Zn _x Sn _1‐x O device achieves a champion power conversion efficiency of 9.28% with an enhanced open‐circuit voltage. These results demonstrate that ultrathin Al ₂ O ₃ interfacial modification provides an effective strategy for mitigating recombination‐related losses in high‐performance Cd‐free Sb ₂ Se ₃ solar cells.

The light–soaking effect in perovskite solar cells (PSCs), while widely observed, presents a complex interplay between performance enhancement and operational instability, the physical origin of which remains insufficiently understood. Herein, based on high–efficiency, large–area modules (21 cm ² ) with certified 23.09% efficiency and 96.29% geometric fill factor, we decouple the underlying mechanisms by combining multi–modal in–situ characterizations with a self–consistent drift–diffusion model that explicitly accounts for coupled ion–electron dynamics. We reveal that light–soaking activation is primarily driven by the cooperative migration of anion (I ⁻ ) and cation (Cs ⁺ ) ions, which selectively accumulate at the respective charge–transporting interfaces. This interfacial ion redistribution fundamentally reconstructs the energy band alignment, enhancing the built–in potential and optimizing charge extraction while passivating interfacial defects. Crucially, we demonstrate that molecular engineering of the hole–transport layer (e.g., employing a phosphonic acid–based self–assembled monolayer) is pivotal for regulating this process, enabling superior ion immobilization and stabilization compared to conventional poly[bis(4‑phenyl)(2,4,6‑trimethylphenyl)amine (PTAA). Based on the state‐of‐the‐art modules, we establish that the activation/deactivation kinetics are intensely dependent on external stimuli (light intensity, spectrum, and temperature), providing a definitive link between operational conditions and device metastability. Our work elucidates the microscopic physico–chemical picture of light–induced performance evolution in PSCs and establishes interface–ion interaction as a central design rule for achieving highly efficient and operationally stable photovoltaics.

Inorganic oxides are widely recognized as stable interfacial materials that can mitigate degradation of perovskite absorbers and prolong device lifetime. However, conventional nickel oxide (NiOx)-based hole-transport layers often suffer from unfavorable energy-level alignment and reactive interfacial defects, while commonly used organic surface modifiers can complicate scalable processing and long-term stability. Here, we introduce cerium iodide (CeI3) as an inorganic interfacial modifier to construct a fully inorganic hole-contact architecture. CeI3 modulates perovskite nucleation and crystallization under ambient processing conditions, producing compact, pinhole-free films with improved coverage. Correlated changes in the oxidation states of Ce, Ni, and Pb after aging, together with reduced iodine loss, support the involvement of Ce species in redox-mediated interfacial regulation. CeI3 modification also improves energy-level alignment and suppresses nonradiative recombination. The resulting devices achieve power conversion efficiencies of 25.19% for 0.113 cm2 cells and 23.37% for 21 cm2 modules, with a geometric fill factor of 98.3%. Encapsulated modules retain 92.3% of their initial efficiency after 1000 h of continuous 1-sun illumination and 95.2% after 1000 h of damp-heat aging at 85 °C/85% RH. Outdoor measurements over one month further demonstrate stable module operation. This ambient-compatible and cost-effective strategy provides a scalable route toward efficient and durable perovskite photovoltaics.

Fullerene-free electron transport layers (ETLs) are highly attractive for lowering the cost and simplifying the fabrication of inverted perovskite photovoltaics, but directly depositing inorganic ETLs on perovskite remains challenging. Here, we develop a low-cost SnO_x-based ETL that can be blade-coated directly onto perovskite films without using C₆₀ or other fullerene-derivative interlayers. Solvent engineering with 1-hexanol prolongs the wet-film lifetime and improves SnO_x film formation, yielding a smooth and compact ETL, while yttrium doping optimizes the interfacial energetics and promotes efficient electron extraction. Consequently, the directly deposited C₆₀-free ETL enables small-area devices with a power conversion efficiency of 19.15% and an open-circuit voltage of 1.06 V. Importantly, this strategy is readily extended to 21 cm² monolithic modules, delivering a champion efficiency of 15.82% with a geometric fill factor of 97.27%. The encapsulated modules retain 91.03% of their initial efficiency after 1000 h of maximum power point tracking at 40 °C and 50% relative humidity and also demonstrate stable outdoor operation over 63 days. These results highlight a practical and scalable route toward low-cost, efficient, and stable C₆₀-free inverted perovskite solar modules.

Scaling perovskite solar cells (PSCs) to large-area, durable modules requires buried interfaces that form uniformly under manufacturing-relevant coating conditions, yet this remains difficult to achieve. Here we report a microflow-driven strategy that enables a bilayer NiOₓ/self-assembled monolayer (SAM) contact in perovskite films processed entirely in ambient air. Evaporation-driven Marangoni recirculation transports π-conjugated SAM molecules to the NiOₓ surface, where strong anchoring promotes dense and uniform coverage. A porous matrix stabilizer homogenizes the solvent vapour flux above the wet film, equalizing the flow field and enabling uniform SAM transport and interfacial assembly over large areas. The resulting inverted rigid PSCs achieve a power conversion efficiency (PCE) of 26.2% (blade-coated, 0.113 cm²), rigid mini-modules achieve a certified PCE of 24.1% (blade-coated, aperture area 20.41 cm²), and flexible large-area modules achieve a certified PCE of 21.13% (slot-die-coated, aperture area 617.4 cm²), placing their performance among the highest reported at these respective scales. Encapsulated modules retain 91% of their initial PCE after 1,000 h of one-sun maximum power point tracking and 93.7% after 1,128 h under damp heat (85 °C/85% relative humidity). These results establish solvent microflow as a controllable lever for scalable, efficient and stable perovskite photovoltaics.