Ji-Seong Hwang

SnO2 is the electron-transport layer (ETL) in record n–i–p perovskite solar cells, grown by chemical bath deposition (CBD) without high-temperature crystallization; whether its crystallinity matters remains unresolved. Here, the same RF-sputtering process on fluorine-doped tin oxide (FTO), at room temperature or 300 °C, yields a predominantly amorphous or an FTO-templated polycrystalline rutile film. The measured film and interface properties anchor a calibrated TCAD model and a thirteen-parameter Sobol global sensitivity analysis (>33,000 simulations), which, unlike one-factor-at-a-time sweeps, resolves the interactions among parameters explicitly. At the film level, crystallinity governs donor activation: UPS, XPS, and STEM-EDS show that the amorphous film holds more fluorine yet has a Fermi level farther below the conduction band, so shallow donors attributed to substitutional fluorine exist in both films but are active only in the crystalline one. At the device level, however, the predicted gain arises from the crystalline film's interface rather than its doping. The Ag/SnO2 contact is rectifying on the amorphous film and ohmic on the crystalline one, through interface-state de-pinning rather than a band-offset shift. The Sobol analysis ranks the SnO2/perovskite interface trap density first (total-effect index ≈ 0.66). A degenerately doped film could screen such traps, but the amorphous film's rectification rules out that route; its deficit is interfacial. At its trap density (∼1013 cm–2), only deep acceptor-like states pin the Fermi level (acceptor-fraction index ≈ 0.83). The predicted crystallization gain is +5.6 pp (20.5 → 26.1%). FAPbI3 half-stack PL/TRPL supports this (1.35× longer lifetime on the crystalline ETL) and bounds that interface's trap density to ≲1012 cm–2. Crystalline growth is one route to the de-pinned interface that CBD ETLs reach chemically, provided that interface is preserved. The absolute efficiencies are calibrated predictions; the benefit's sign and the lever ranking are robust.

C ₆₀ -buffered SS-based PSCs maintain efficiency and stability under bending, enabling flexible BIPV and VIPV applications.

As we move towards the commercialization and upscaling of perovskite solar cells, it is essential to fabricate them in ambient environment rather than in the conventional glove box environment. The efficiency of ambient-processed perovskite solar cells lags behind those fabricated in controlled environments, primarily owing to external environmental factors such as humidity and temperature. In the case of device fabrication in ambient environments, relying solely on a single parameter, such as temperature or humidity, is insufficient for accurately characterizing environmental conditions. Therefore, the dew point is introduced as a parameter which accounts for both temperature and humidity. In this study, a machine learning model was developed to predict the efficiency of ambient-processed perovskite solar cells based on meteorological data, particularly the dew point. A total of 238 perovskite solar cells were fabricated, and their photovoltaic parameters and dew points were collected from March to December 2023. The collected data were used to train various tree-based machine learning models, with the random forest model achieving the highest accuracy. The efficiencies of the perovskite solar cells fabricated in January and February 2024 were predicted with a MAPE of 4.44%. An additional Shapley Additive exPlanations analysis confirmed the significance of the dew point in the performance of perovskite solar cells.

This study investigated the integration of perovskite solar cells (PSCs) on stainless steel (SS) substrates for application in building-integrated photovoltaics (BIPV). Using advanced atomic force microscopy measurements, we confirmed that enhanced substrate roughness increased the reflectance along an interface. Consequently, a remarkable final efficiency of 11.9% was achieved. Notably, PSCs, known for their exceptional efficiency of 26.1%, can overcome the inherent efficiency limitations of SS-based thin-film solar cells. In this study, a PSC with an efficiency of 14% was fabricated on a flexible SS substrate. This study is a significant step towards advancing sustainable energy solutions for BIPV applications. The global shift towards renewable energy sources has catalyzed intensive research and development efforts, rendering the exploration of alternative materials and manufacturing processes a priority. The success of PSCs on SS substrates underscores their promise to achieve a balance between efficiency and versatility in BIPV solutions. Moreover, our findings reveal that controlling the substrate surface characteristics can significantly enhance the performance of PSCs, offering a pathway toward greater energy efficiency and sustainability in the construction industry.