Sang Il Seok

Surface texturing in crystalline silicon solar cells imposes a fundamental trade‐off in perovskite‐silicon tandems: micrometer‐scale pyramids enable efficient light trapping but limit the conformal deposition of thin perovskite films with sub‐micrometer thickness, whereas reduced texture heights improve compatibility at the expense of optical performance and interfacial quality of the tandem device. Here, we address this challenge by combining precisely controlled submicron texturing with an ozone‐assisted chemical rounding treatment. The resulting silicon substrates feature smoothly rounded, symmetric submicron textures that suppress micro‐terrace formation and partial epitaxy at the amorphous silicon/crystalline silicon interface, while promoting more spatially uniform optoelectronic properties in the subsequently integrated top‐cell stack. The morphology‐engineered texture yields a monolithic perovskite–silicon tandem device with a power conversion efficiency of 33.25%, demonstrating that multiscale morphological control provides a powerful pathway to simultaneously improve the optical performance and interfacial quality of tandem solar cells.

Efficient wide‐bandgap (WBG) perovskite solar cells (PSCs) have propelled the rapid advancement of perovskite (PVK) tandem solar cells (TSCs). However, their commercialization remains impeded by the intrinsic instability of WBG PSCs, particularly under high‐temperature maximum power point tracking conditions, underscoring the urgent need to develop robust, high‐performance WBG top‐cell materials. Here, we first summarize strategies to enhance the device performance of mainstream WBG metal halide PSCs, highlighting advances achieved through interface engineering, additive engineering, and related approaches. Then we evaluate the potential of metal chalcogenides solar cells as top‐cell candidates, identifying their high processing temperatures as a key factor that constrains their integration in TSCs. Finally, we propose metal chalcohalides as promising top‐cell materials for TSCs, owing to their suitable bandgaps, low toxicity, superior stability, and moderate processing temperatures. This review aims to provide design guidelines for the development of next‐generation WBG top‐cell materials in TSCs.

The complex moisture–oxygen environment in air places stringent demands on surface passivation for air‐processed perovskite solar cells. However, most conventional ammonium ligand‐based passivation, which binds to the perovskite surface through a terminal site, often induces ligand intercalation, elevates interfacial resistance, and compromises environmental stability, thereby limiting efficient device fabrication under ambient conditions. In this study, we report a robust, ligand‐based, intermediate‐site anchoring strategy for nonlayered interfacial passivation using a series of choline derivatives. The thioacyl sulfur coordinates strongly with under‐coordinated Pb ²⁺ sites, while iodide counter‐anions assist in halide vacancy healing, collectively forming a thermally robust and electronically homogeneous top interface. The surface passivation homogenizes surface potential, optimizes band alignment, relaxes residual strain, and suppresses trap‐assisted recombination and halide migration. Consequently, the resulting perovskite solar cells achieve a power conversion efficiency (PCE) of 26.54%, the highest value for air‐processed n–i–p PSCs reported so far. These devices also retained over 90% PCE after 2000 h at 65°C and 90% under continuous maximum power point tracking for 1000 h (AM 1.5G, 40°C ± 1°C), with projected T ₈₀ lifetimes of ∼9800 h under illumination and ∼11 000 h under thermal aging, among the most stable air‐processed perovskite solar cells reported to date.

Perovskite/Si tandem (PST) cells have recently achieved record‐breaking efficiencies, positioning them as a leading technology in next‐generation photovoltaics. However, maintaining long‐term operational stability and ensuring consistent performance under realistic fabrication and deployment conditions remain critical challenges. To overcome these issues, we propose a dual optimization strategy that integrates electrical interface engineering with tailored optical design. First, we introduce a novel self‐assembled monolayer containing a propoxyphenyl‐based linker, which enhances molecular packing density and significantly increases the shunt resistance of the device. This interface modification improves hole selectivity and broadens fabrication tolerance by increasing the allowable range of current mismatch between sub‐cells while maintaining high efficiency. Second, we design a light‐scattering film by embedding shape‐controlled phosphor particles into a textured poly(dimethylsiloxane) (PDMS) matrix, which improves light harvesting through UV down‐conversion and diffuse transmission. As a result, we achieve a PCE of 31.66% for a 1 cm ² device. These findings demonstrate a synergistic design approach and offer a practical route toward robust, high‐efficiency PST devices with improved fabrication tolerance.

Inkjet printing (IJP) is a promising technique for achieving uniform, large-area deposition of perovskite films. Although IJP offers several advantages in processability and scalability that are highly attractive for industrial manufacturing, systematic studies employing in-line controlled inkjet printing systems remain scarce. Here, we demonstrate the deposition of approximately 700 nm-thick perovskite films by IJP at a relative humidity (RH) of 55% in an air atmosphere. We found that the quenching pathway of the wet perovskite film strongly influences the resulting film morphology and crystallographic characteristics. By optimizing this process, we successfully fabricated self-assembled monolayer-incorporated wide-bandgap perovskite films with a dominant (110) crystallographic orientation using IJP. As a result, we achieved over 20% efficiency in a 1.69 eV bandgap perovskite solar cell, which is suitable for silicon−perovskite tandem integration.

Additives and passivators are commonly used to regulate crystallization and suppress defects in halide perovskites. However, existing additives or passivation agents struggle to concurrently achieve effective defect passivation and efficient charge transport, and their passivation effects often fail to endure throughout device fabrication and operation. Here, we systematically screened a series of redox‐active, bifunctional passivation molecules with various functional motifs, namely sildenafil (SDNF), avanafil (AVNF), and dabrafenib (DRFN), to achieve spatial defect passivation and temporal redox healing in perovskite films. Spatially, the sulfonyl (‐SO ₂ ‐) group and heterocyclic nitrogen of DRFN coordinate with perovskites at dual sites, enabling parallel binding to multiple Pb ²⁺ centers. Temporally, its sulfonyl group exhibits moderate electron‐withdrawing capability, facilitating redox‐mediated defect healing by reducing metallic Pb ⁰ species. These combined effects yield peak power conversion efficiencies of 25.28% in the n‐i‐p configuration and 26.62% in the p‐i‐n configuration, along with exceptional thermal and operational stability. The unencapsulated device efficiency shows almost no degradation after 1200 h under continuous maximum power point tracking.