https://scholar.dgist.ac.kr/handle/20.500.11750/69 2026-07-14T06:39:50Z https://scholar.dgist.ac.kr/handle/20.500.11750/60422 Title: Enhanced Wide-Bandgap Perovskite Solar Cells via Kinetically Optimized C60 Electron-Transport Layers Author(s): Kumar, Naveen; Jo, Hyo Jeong; Son, Dae-Ho; Lee, Jaebaek; Ali, Amanat; Kang, Jin-Kyu; Yang, Kee-Jeong; Sung, Shi-Joon; Jeong, Hyeonjong; Cho, Chang-Hee; Kim, Dae-Hwan; Hwang, Dae-Kue Abstract: High-efficiency tandem solar cells require wide-bandgap (WBG) perovskites as the top absorber, yet such devices often suffer severe nonradiative recombination, voltage losses, and halide segregation. This work demonstrates that carefully controlling the deposition kinetics of the fullerene electron-transport layer (ETL) offers an elegant route to overcome these issues without complex passivation strategies. WBG perovskite solar cells using a FA(0)(.8)Cs(0)(.2)Pb(I0.8Br0.2)(3) absorber were fabricated in a p-i-n architecture with C-60 ETLs deposited at three different evaporation rates. When the C-60 deposition rate was slowed to 0.1 & Aring; s(-1), our devices achieve a 20.4% PCE with a relatively low Voc deficit (~0.48 eV) without complex molecular passivation, 2D/3D heterostructures, or multistep surface reconstruction. The improvement originates from suppressed nonradiative recombination and reduced shunt leakage: The slow-deposited C-60 film yields a higher open-circuit voltage (~1.17 V), increased fill factor (80%), and reduced saturation current density and trap-state density compared with faster deposition. Photoluminescence, impedance spectroscopy, and transient photovoltage analyses reveal that slower deposition produces a compact and well-ordered C-60 layer which minimizes trap-assisted recombination, decreases Urbach energy (16.68 meV), and lowers the ideality factor (n approximate to 1.33). Structural characterizations confirm improved C-60 molecular interface and smoother morphology at slow deposition rates. This work provides a simple processing guideline for high-performance WBG perovskite solar cells and offers valuable insights for scalable tandem cell fabrication. 2026-03-31T15:00:00Z https://scholar.dgist.ac.kr/handle/20.500.11750/60224 Title: Self-Hybridized Multimodal Exciton-Polaritons in All-Inorganic Lead Halide Perovskite Microcrystals Author(s): Maqbool, Faisal; Tahir, Zeeshan; Rashid, Mamoon Ur; Sheeraz, Muhammad; Cho, Chang-Hee; Kim, Yong Soo Abstract: Exciton-polaritons are potential avenues for quantum fluids of light and hold great promise for future all-photonic integrated circuits and devices. Herein, self-hybridized multimodal exciton polaritons are investigated in all-inorganic lead halide perovskite microplatelets grown via the space-limited antisolvent crystallization method. Interestingly, the as-grown microcrystals not only exhibit robust excitons at room temperature but also form a photonic microcavity, providing a self-sufficient platform for strong exciton-photon coupling. Resultantly, multiple parabolic dispersions were observed in the angle-resolved photoluminescence mappings, each with a characteristic curvature flattening at large momentum, signifying multimodal polariton formation. The corresponding theoretical fits reveal considerably large Rabi-splitting values of ∼360, 336, and 320 meV for microplatelets of various thicknesses. Such large splitting is attributed to the high (∼perfect) spatial overlap between the excitonic medium and the photonic mode’s electric field. In addition, the variation in the Rabi-splitting as a function of microcrystal thickness demonstrates the facile modulation of exciton-photon coupling strength in self-hybridized systems. Besides, the distinct excitonic and photonic contents of the individual parabolic dispersions suggest the coexistence of polaritons with different compositions. Thus, our results demonstrate a straightforward platform for the realization and manipulation of strong coupling phenomenon crucial for polariton device applications. 2025-12-31T15:00:00Z https://scholar.dgist.ac.kr/handle/20.500.11750/60022 Title: Comparative analysis of macroscopic and microscopic optical absorbance in hemagglutination assay Author(s): Jeon, Dong-Gyu; Lee, Chung-Young; Cho, Chang-Hee; Lee, Gang Ho; Chang, Yongmin; Nam, Sung-Wook Abstract: We report a comparative study of macroscopic and microscopic optical absorbance in hemagglutination (HA) assay. Red blood cells (RBCs) exhibit unique optical absorbance properties with characteristic peaks including Soret, Qv, and Qo. In addition, RBCs absorb light and appear as dark contrast in bright-field microscopy images, indicating an increase in local optical density (OD). By systematic analysis of macroscopic and microscopic OD measurements and UV-Visible (UV-Vis) spectroscopy, we developed a phenomenological model of RBC agglutination and non-agglutination. The antigen-antibody reaction in RBC agglutination behaves as a catastrophic event such that networking of RBC clumps is initiated at a critical RBC concentration. We analyzed the dependence of OD on RBC concentration. At the critical RBC concentration, OD values are dropped or saturated for RBC agglutination, on the other hand, ODs keep increasing as the increase of RBC concentration for RBC nonagglutination. By the analysis of UV-Vis spectroscopy for HA assay, we provide an optimal wavelength range as 480-520 nm, away from RBC characteristic absorption peaks. For further validation, we demonstrated the ODbased HA assay for the detection of H1N1 influenza A virus. Our investigation provides insights into how to utilize the physical properties of RBCs for novel HA assay platforms. 2025-11-30T15:00:00Z https://scholar.dgist.ac.kr/handle/20.500.11750/59984 Title: Enhancing CO2-to-CH4 conversion efficiency of TiO2 through synergistic morphology tuning, defect engineering, and heterojunction formation Author(s): Kim, Dongyun; LEE, Kyuseok; Park, Young Ho; Lee, Junho; Murali, Guntakrinda; In, Insik; In, Su-Il; Lee, Jeonghyeon; Shin, Chaelin; Jeong, Hyeonjong; Cho, Chang-Hee; Lee, Seung Jun Abstract: The photocatalytic reduction of CO2 into valuable fuels represents a promising pathway toward sustainable energy solutions. In this study, the CO2-to-CH4 conversion efficiency of TiO2 is enhanced by implementing synergistic strategies, including morphology tuning, defect engineering, and composite construction. Reduced TiO2 nanosheet (2D-RT) morphology is employed to construct the ternary composite photocatalyst, Cu/reduced graphene oxide/2D-RT (Cu/G/2D-RT), which outperforms 2D-RT, P25 derived reduced TiO2 (P-RT), and Cu/G/P-RT. The CH4 production rate of Cu/G/2D-RT is nearly 62 times that of P-RT and 3.4 times that of Cu/G/P-RT. The optimal defect concentration in 2D-RT improves visible light absorption and charge separation, while the 2D structure enhances interaction with rGO, leading to better charge transport. Additionally, single-electron-trapped oxygen vacancies accelerate water oxidation, producing more protons to enhance the CO2 reduction on Cu cocatalyst. The CO2 reduction significantly improved under multi-sun illumination. However, the repeated cycling led to catalyst degradation, primarily driven by partial reduction of Cu. The in-situ diffuse reflectance infrared Fourier transform spectroscopy reveals the CO2 conversion pathway. Importantly, the results demonstrate that while a high defect concentration in TiO2 enhances visible light absorption, it does not necessarily ensure enhanced charge separation, optimal band alignment in heterojunctions, and improved CO2 reduction efficiency. 2025-12-31T15:00:00Z