Yonghwan Lee

Fluorine-free transparent photovoltaic backsheets were developed via dip-coating polyethylene terephthalate (PET) films with perhydropolysilazane (PHPS), which were subsequently converted to a SiO x N y-based inorganic coating layer on the PET surface. Fourier-transform infrared (FT-IR) spectroscopy confirmed the formation of Si-O, SiN , and Si-OH bonds, effectively converting the PHPS precursor into a robust SiO x N y network. UV-Vis measurements revealed that the optical transmittance of the coated films was high (>88%), ensuring optical suitability for photovoltaic transparent backsheet applications. The water vapor transmission rate (WVTR) measurements demonstrated that the moisture permeability (<2 g/m 2 •day) was lower than that of the untreated PET films, whereas the adhesion tests confirmed strong interfacial bonding between the SiO x N y-coated PET film and the encapsulant. Furthermore, the films retained high transparency and strong moisture barrier performance after accelerated aging under pressure-cooker test (PCT) conditions and UV irradiation, confirming their high durability and environmental stability. Overall, SiO x N y-coated PET films are a sustainable, transparent, and high-performance alternative to conventional fluorine-based backsheets for low-carbon photovoltaic modules.

In space applications, photovoltaic cells, which are used to provide power and enable the self-operation of satellites, are exposed to various extreme stressors. Among these, electron radiation induces various defects in photovoltaic cells, thereby accelerating performance degradation. To mitigate radiation-induced damage, effective shielding methods must be integrated into the photovoltaic module. In this study, we investigated aluminum-doped zinc oxide (AZO) thin-film-coated quartz glass as a potential radiation-shielding cover glass for III–V multi-junction space photovoltaic cells. To enhance the shielding performance, two post-treatment methods, ultraviolet (UV) treatment and thermal annealing, were tested. It was observed that thermal annealing improved the crystallinity of the AZO film and enhanced its effective shielding against electron radiation. Under electron irradiation at 1.2 MeV with a fluence of 1 × 10¹⁵ to 3 × 10¹⁵ e⁻ cm⁻², the thermally annealed AZO-coated glass demonstrated superior radiation-shielding performance compared to bare quartz glass. Consequently, when applied to our in-house-developed space photovoltaic modules incorporating a 4G32C III–V photovoltaic cell, they resulted in an improvement in efficiency degradation, from 4.18% to 2.37%, after electron irradiation at 1.2 MeV and 1 × 10¹⁵ e⁻ cm⁻². These findings demonstrate that AZO thin films, when prepared with appropriate post-treatment, can serve as reliable radiation-shielding layers, offering significant potential enhancement to the long-term durability and operating stability of space photovoltaic modules.

In this study, we introduce a microscale periodic surface structuring on (100)-oriented GaAs semiconductor substrates via a controlled cracking technology. This method circumvents the need for costly photolithography and etching, enabling the direct formation of highly periodic microscale V-shaped groove structures on GaAs substrates. By systematically varying the thickness of the tensile-stressed Ni stressor layer of the controlled cracking process, we achieved precise control over the morphology of the groove structures, including their pitch, amplitude, and inclination angle. Density functional theory (DFT) calculations were employed to investigate the critical energy release rates across various crystalline planes, providing valuable insights into the modifications observed in the fracture structures. Optical simulations demonstrated that the inclination angle is the predominant factor influencing the optical reflection, while the pitch of the groove structure exerts a minimal effect. Furthermore, pronounced anisotropic wetting properties were observed on the spalled GaAs substrates with the degree of anisotropy enhanced by increasing the dimensions of the V-shaped grooves. This cracking-assisted surface structuring method constitutes a significant advancement over traditional patterning techniques, offering a cost-effective and efficient strategy for surface structuring with broad potential applications in optoelectronics and wetting-related technologies.

III‐V semiconductors are favoured photo absorber materials for solar energy conversion due to their ideal bandgap, yet their high‐cost hinders widespread adoption. Utilizing thin films of these semiconductors presents a viable way to address the cost‐related challenges. Here, a novel mechanical exfoliation technique is demonstrated, also known as controlled spalling, as a cost‐effective and facile way to obtain thin films of III‐V semiconductors. As a proof of concept, 15 μm thick InP films are successfully exfoliated from their original wafers. Thorough characterization using cathodoluminescence and photoluminescence spectroscopy confirms that the opto‐electronic properties of the exfoliated InP films remain unaffected. Utilizing these InP thin films, InP thin‐film heterojunction solar cells with efficiencies exceeding 13% are demonstrated. Additionally, InP photoanodes are fabricated by integrating NiFeOOH catalyst onto these InP thin‐film solar cells, achieving an impressive photocurrent density of 19.3 mA cm⁻² at 1.23 V versus reversible hydrogen electrode, along with an applied bias photon‐to‐current efficiency of ≈4%. Overall, this study showcases the efficacy of controlled spalling in advancing economically viable and efficient III‐V semiconductor‐based solar energy conversion devices.