Kwanyong Seo

Biocatalytic semi-artificial photosynthesis enables selective solar-to-chemical conversion by harnessing photoelectrocatalytic platforms to drive redox biocatalysis. However, the reliance of most photoelectrochemical (PEC)-based devices on transparent conductive oxides (TCOs) or wired configurations introduces resistive losses and architectural complexity, limiting the translation of biosolar conversion beyond laboratory-scale systems. Here, we report a wireless, monolithic semi-artificial leaf device toward scalable and practical solar biosynthesis. The PEC tandem, composed of a poly(ethylene glycol) (PEG)-modified BiVO4 (PEG:BiVO4) photoanode and a tunnel-oxide-passivated-contact (TOPCon) Si photovoltaic (PV), supplies sufficient photovoltage to reduce O2 to H2O2 on an anthraquinone-2-carboxylic acid (AQC)-functionalized carbon-fiber paper (CFP) cathode under solar light, sustaining over 100 h of stable operation. The photogenerated H2O2 reacts with peroxygenases to catalyze the oxyfunctionalization of substituted benzenes, alkanes, and fatty acids with record-high total turnover numbers of 166,100 (unspecific peroxygenase) and 3,700 (cytochrome P450). Furthermore, the scaling of the PEC device allows the direct conversion of natural light into enantiopure alcohols.

Two-dimensional (2D) heterostructures composed of transition metal dichalcogenides (TMDCs) are promising materials for next-generation electronics and optoelectronics due to their unique electronic and optical properties. Although 2D TMDC heterostructures with coexisting vertical and lateral junctions are highly desirable for both fundamental research and technological applications, they have rarely been explored. Here, we report for the first time the synthesis of 2D heterostructures with coexisting vertical and lateral junctions composed of MoSe₂ and WSe₂. Monolayer MoSe₂ is first synthesized on a substrate due to its lower thermodynamic formation energy followed by the growth of monolayer WSe₂ on both the basal plane and edges of MoSe₂, thereby forming MoSe₂-WSe₂ heterostructures with coexisting vertical and lateral junctions. These heterostructures are characterized using various analytical techniques. We investigated nonlinear optical (NLO) properties using harmonic generation measurements to determine the crystal orientation of star-shaped MoSe₂-WSe₂ heterostructures. In addition, we investigated the junction geometry-dependent NLO responses of the vertical and lateral heterojunctions over a broad spectral range to demonstrate their resonant features and interlayer coupling effects. Furthermore, we fabricated electronic devices using these heterostructures and compared the diode characteristics of the vertical and lateral p-n junctions. These MoSe₂-WSe₂ heterostructures with coexisting vertical and lateral junctions are advanced materials for 2D electronics, optoelectronics, and nonlinear optical applications.

Efficient management of incident light─maximizing absorption while suppressing reflection─is essential for sustaining the power conversion efficiency (PCE) of solar cells under real operating conditions. However, since the position of the sun changes depending on the season and time of day, the light absorption in solar cells fluctuates, decreasing as the angle of incidence increases. To maximize solar power generation, it is therefore essential to mitigate angle-induced light absorption losses. In this study, we employed crystalline silicon microwire arrays to enhance light trapping and reduce incidence-angle-dependent losses. Additionally, transparent, light-scattering silica beads were inserted layer by layer using the Langmuir-Blodgett dip-coating technique, which enabled systematic control of bead thickness from a monolayer to sextuple layers. Among these, the double-layer configuration was found to be optimal, yielding the highest photocurrent density and efficiency. The PCE of planar solar cells decreased by over 38.1% when the incident angle increased from 0° to 50°, whereas the PCE of the solar cells with microwires and silica beads in between decreased by less than 11.9%. Notably, outdoor seasonal calculations revealed that the silica bead integrated structure achieved a cumulative power output of 36.09 MJ/m², corresponding to 27.5 and 7.4% improvements compared to planar and microwire cells, respectively, thereby validating its practical applicability. This work provides a simple and effective strategy to reduce the angular dependence of PCE degradation in solar cells.

A bioinspired self-cleaning strategy for solar cells has been proposed to enable the automatic removal of dust deposited on surfaces. However, the presence of oil-based sticky residues from volatile organic compounds poses a significant challenge for water-based cleaning methods. In this study, we introduce oil-repelling surfaces capable of self-cleaning in any orientation to address oily dust contamination. The proposed surface features a disconnected grid pattern with domed top surfaces and hyperbolic sidewalls. The hyperbolic sidewalls contribute to superomniphobicity, while the domed top surfaces minimize oil adhesion and enhance the efficiency of photovoltaic cells. Additionally, the disconnected grid structure enhances lateral liquid repellency, achieving higher contact angles compared to connected grid designs. When applied to thin-film crystalline silicon solar cells, the surface texture enhances photovoltaic efficiency through the light-scattering effect of the lens-shaped features. Furthermore, the proposed surface demonstrates mechanical stability under repeated bending.

Transparent photovoltaics (TPVs) hold immense promise for applications where aesthetic appeal and functional performance align, such as building‐integrated photovoltaics. Among TPV technologies, crystalline silicon ( c ‐Si) TPVs have emerged as a leading candidate owing to their glass‐like transparency, high efficiency, and long‐term stability. However, their overall performance is limited by light loss in transparent regions, which necessitates strategies to maximize light absorption in the active c ‐Si areas. In this study, a straightforward yet effective approach is presented to enhance light absorption in c ‐Si TPVs by forming random micro‐pyramid structures on the c ‐Si surface via a simple wet‐chemical process. These surface structures significantly improve light absorption without compromising visual transparency. This improvement translates into record short‐circuit current density ( J _SC ) of 32.7 mA cm ⁻² for a 1 cm ² device. When scaled up to a 25 cm ² device, the J _SC further increases to 33.3 mA cm ⁻² , achieving an efficiency of 16.1%, which is the highest reported value to date for neutral‐colored TPVs with an average visible transmittance (AVT) of 20%. These results demonstrate a scalable and cost‐effective method to advance TPV performance, paving the way for broader commercial applications of high‐efficiency, transparent solar technologies.

Propylene oxide (PO) is a key industrial chemical, often produced by epoxidizing propylene with H₂O₂ over titanium silicalite-1. However, current H₂O₂ production via the anthraquinone process relies on fossil-derived hydrogen, leading to substantial CO₂ emissions. Sustainable PO synthesis requires green H₂O₂ production. Here, we present a fully unassisted, solar- and bias-free system that generates H₂O₂. This platform enables modular, eco-friendly on-site PO synthesis by coupling formaldehyde oxidation with two-electron O₂ reduction under alkaline conditions. Efficient propylene epoxidation under these conditions is achieved using titanium silicalite-1 modified by introducing dinuclear titanium sites with Ti–O–Ti bonds, as revealed by density functional theory and instrumental analyses. The unassisted H₂O₂ production system is integrated with the modified titanium silicalite-1 to realize continuous PO production (1657 μmol_PO cm⁻² over 24 h), without electric or solar energy input. This unassisted PO production method can thus be energy-independent, offering a sustainable alternative to conventional processes.

The photoelectrochemical nitrate reduction reaction (PEC NO₃RR) potentially converts nitrate, a major water pollutant, into NH₃, which is an eco‐friendly, next‐generation energy source. However, achieving high efficiency in the PEC NO₃RR has been challenging because of the need for high applied voltage and competition with the hydrogen evolution reaction (HER). In this study, a PEC NO₃RR is successfully implemented that demonstrated a high NH₃ production rate of 2468 µg cm⁻² h⁻¹ (at −0.1 V vs RHE) using a c‐Si photocathode with Ni foil as the catalyst. Conducting the PEC NO₃RR under alkaline conditions can lead to the self‐activation of the Ni surface with Ni(OH)₂. Ni(OH)₂ can suppress the competitive HER and facilitate NO₃RR, enhancing NH₃ production efficiency. Furthermore, a PEC NO₃RR system is developed that operates without external voltage and achieved bias‐free record‐high solar to NH₃ conversion efficiency of 3.8% and an NH₃ production rate of 554 µg cm⁻² h⁻¹.

To commercialize the technology of photoelectrochemical hydrogen production, it is essential to surpass the US. Department of Energy target of 0.36 mmol h⁻¹ cm⁻² for 1-sun hydrogen production rate. In this study, we utilize crystalline silicon, which can exhibit the highest photocurrent density (43.37 mA cm⁻²), as the photoelectrode material. However, achieving bias-free water splitting (>1.6 V) remains challenging due to the intrinsic low photovoltage of crystalline silicon (0.6 V). To address this limitation, we replace water oxidation with low-potential furfural oxidation, enabling not only bias-free hydrogen production but also dual hydrogen production at both the cathodic and anodic sides. This approach results in a record 1-sun hydrogen production rate of 1.40 mmol h⁻¹ cm⁻², exceeding the Department of Energy target by more than fourfold.

Transparent solar cells maximize installation space by being applicable to glass areas such as building windows and sunroofs, necessitating high power conversion efficiency (PCE), long‐term stability, and aesthetic appeal. This study demonstrates the development of transparent crystalline silicon ( c ‐Si) solar cells that exhibit vivid colors, enhanced PCE, and long‐term stability. To achieve vivid coloration, a metal‐oxide‐based color filter with a single metal layer and TiO ₂ thin films, which show high transmittance, is integrated into the neutral‐colored transparent c ‐Si solar cells. As a result, the proposed all‐inorganic‐based transparent solar cells exhibited red, green, and blue colors, achieved a high PCE of 15.3%, and demonstrated long‐term stability for up to 1000 h by leveraging c ‐Si solar cells in conjunction with all inorganic color filters.