Yong Chan Choi

A stage-gated, orientation-first roadmap for quasi-one-dimensional (quasi-1D) photovoltaics is presented, translating the established Sb ₂ S ₃ developmental trajectory to the emerging SbSI family (SbSI, SbSeI, BiSI, and related alloys). The focus is on chain- or ribbon-based absorbers, where charge extraction is governed by thin-film texture and microstructural orientation rather than by interface engineering alone. Sb ₂ S ₃ is established as a quantitative reference system to define the structural basis of an orientation-first design logic, in which a texture coefficient (TC) threshold for extraction-aligned planes (TC(hk1) > 2) is treated as a causal prerequisite for high performance. The transferability boundary between the purely covalent Sb ₂ S ₃ framework and iodide-containing SbSI-family chalcohalides is delineated, framing SbSI development as an explicit validity test of the "Sb ₂ S ₃ -like stability" assumption. A key differentiator is the possibility of halide-ion motion under operating bias, which can shift SbSI from a rigid, vacancy-limited regime to a perovskite-like, ion-migrating regime requiring bias-tolerant device architectures and ion-suppression strategies. The roadmap condenses transferable model rules into a five-gate cascade: (i) film-formation pathways; (ii) an orientation-engineering toolbox; (iii) architecture selection; (iv) defect–stability classification; and (v) extension to SbSeI and Bi-containing alloys. To bridge laboratory Technology Readiness Levels (TRL) with industrial Scale Readiness Levels (SRL), manufacturability checkpoints based on established thin-film standards are embedded. Finally, indoor energy harvesting at ~1000 lux is positioned as a validation gate for leakage suppression, treated as a prerequisite for outdoor durability and energy-autonomous Internet of Things (IoT) deployment.

Nanoporous anodic alumina (nPAA) films formed on aluminum in lower aliphatic carboxylic acids exhibit blue self-coloring and characteristic properties such as photoluminescence (PL), electroluminescence, and electron spin resonance. The blue colors are seemingly originated from the adsorbed radicals incorporating into the oxide during the aluminum anodization. However, there is lack of reports revealing the detailed activation mechanism of the adatoms in the complexes. This study investigates the blue PL and its correlation with the atomic and electronic structures of the active aluminum surface using multiple theoretical and experimental methods. The results show that the concentration of carboxylates at the nPAA surface is highly correlated with the blue colorization and manifest that unpaired electrons in carbon (derived from the carboxylates) bridging two aluminum atoms at surface can play as an active source of the blue colorization. Therefore, it is suggested that controlling the adsorption of the carboxylate on the alumina membrane having large surface-to-volume ratio can be an efficient way to generate the blue light for the optoelectronic applications.

Solar cell technology is an effective solution for addressing climate change and the energy crisis. Therefore, many researchers have investigated various solar cell absorbers that convert Sunlight into electric energy. Among the different materials researched, heavy pnictogen chalcohalides comprising heavy pnictogen cations, such as Bi³⁺ and Sb³⁺, and chalcogen-halogen anions have recently been revisited as emerging solar absorbers because of their potential for efficient, stable, and low-toxicity solar cell applications. This review explores the recent progress in the applications of heavy pnictogen chalcohalides, including oxyhalides and mixed chalcohalides, in solar cells. We categorize them into material types based on their common structural characteristics and describe their up-to-date developments in solar cell applications. Finally, we discuss their material imitations, challenges for further development, and possible strategies for overcoming them.

Ternary chalcohalides are promising lead-free photovoltaic materials with excellent optoelectronic properties. We propose a simple one-step solution-phase precursor-engineering method for antimony selenoiodide (SbSeI) film fabrication. SbSeI films were fabricated by spin-coating the precursor solution, and heating. Various precursor solutions were synthesized by adjusting the molar ratio of two solutions based on SbCl₃-selenourea and SbI₃. The results suggest that both the molar ratio and the heating temperature play key roles in film phase and morphology. Nanostructured SbSeI films with a high crystallinity were obtained at a molar ratio of 1:1.5 and a temperature of 150 °C. The proposed method could be also used to fabricate (Bi,Sb)SeI.

Despite their comparable performance to commercial solar systems, lead-based perovskite (Pb-perovskite) solar cells exhibit limitations including Pb toxicity and instability for industrial applications. To address these issues, two types of Pb-free materials have been proposed as alternatives to Pb-perovskite: perovskite-based and non-perovskite-based materials. In this review, we summarize the recent progress on solar cells based on antimony/bismuth (Sb/Bi) chalcohalides, representing Sb/Bi non-perovskite semiconductors containing chalcogenides and halides. Two types of ternary and quaternary chalcohalides are described, with their classification predicated on the fabrication method. We also highlight their utility as interfacial layers for improving other solar cells. This review provides clues for improving the performances of devices and design of multifunctional solar systems.

Pb-based hybrid perovskite solar cells, despite their advantages, face challenges in commercialization. In recent years, Bi-based chalcohalides are being considered as potential alternative candidates, however, their current device efficiency remains unsatisfactory. Herein, a two-step solution method is developed and applied to the fabrication of BiSI films. The method consists of the formation of Bi₂S₃ (step I) and its conversion to BiSI (step II). The Bi₂S₃ was fabricated by a thiol-amine solution process and the BiSI conversion was achieved by chemical reaction between the as-formed Bi₂S₃ and BiI₃. It was found that the formation of BiSI was highly dependent on the Bi:S molar ratio of the Bi₂O₃-thiourea solution and the number of times of step I. The as-fabricated BiSI film had an optical band gap of 1.61 eV and exhibited nanorod morphology. In addition, the electronic structure is explored and discussed for solar cells applications.

Tin sulfide (SnS) is one of the most promising solar cell materials, as it is abundant, environment friendly, available at low cost, and offers long‐term stability. However, the highest efficiency of the SnS solar cell reported so far remains at 4.36% even using the expensive atomic layer deposition process. This study reports on the fabrication of SnS solar cells by a solution process that employs rapid thermal treatment for few seconds under Ar gas flow after spin‐coating a precursor solution of SnCl₂ and thiourea dissolved in dimethylformamide onto a nanostructured thin TiO₂ electrode. The best‐performing cell exhibits power conversion efficiency (PCE) of 3.8% under 1 sun radiation conditions (AM1.5G). Moreover, secondary treatment using SnCl₂ results in a significant improvement of 4.8% in PCE, which is one of the highest efficiencies among SnS‐based solar cells, especially with TiO₂ electrodes. The thin film properties of SnS after SnCl₂ secondary treatment are analyzed using grazing‐incidence wide‐angle X‐ray scattering, and high‐resolution transmittance electron microscopy.