The reactive ion etching (RIE) technology which enables nano-texturatization of surface is applied on monocrystalline silicon solar cell. The additional RIE process on alkalized textured surface further improves the blue response and short circuit current. Such parameter is characterized by surface reflectance and quantum efficiency measurement. By varying the RIE process time and matching the subsequent processes, the absolute efficiency gain of 0.13% is achieved. However, the result indicates potential efficiency gain could be higher due to process integration. The critical etch process time is discussed which minimizes both front surface reflectance and etching damage, considering the challenges of required system throughput in industry.

Various wt. ratios of indium were doped to the poly(3,4-ethylenedioxythiophene)-poly(styreneswulfonate) (PEDOT:PSS) to enhance the conductivity and transmittance. The transmittance of the films increased with increasing the amount of indium. The field emission scanning electron microscope (FESEM) image of 2.54 wt. % of indium doped PEDOT:PSS film shows large number of aggregated indium particles. However, more than 2.54 wt. % of indium doped PEDOT:PSS films showed reduced aggregated indium particles. Moreover, 4.47 wt. % of indium doped PEDOT:PSS film showed no aggregated particles. The resistivity of pure PEDOT:PSS film showed $880k{\Omega}{\cdot}cm$. The resistivity of 1.03 wt. % indium doped film reduced approximately 26 times compared with pure PEDOT:PSS film. The resistivity of indium doped film further reduced with increasing the amount of indium, which showed approximately $0.55k{\Omega}{\cdot}cm$ for the PEDOT:PSS film doped 4.47 wt. % of indium.

The researches on the silicon-based thin films are being actively carried out. The silicon-based thin films can be made as amorphous, microcrystalline and mixed phase and it is known that the optical bandgap can be controlled accordingly. They are suitable materials for the fabrication of single junction, tandem and triple junction solar cells. It can be used as a doping layer through the bonding of boron and phosphorus. The carbon and oxygen can bond with silicon to form a wide range of optical gap. Also, The optical gap of hydrogenated amorphous silicon germanium can be lower than that of silicon. By controlling the optical gaps, it is possible to fabricate multi-junction thin film silicon solar cells with high efficiencies which can be promising photovoltaic devices.

As a promising solution to global warming and growing energy demand, photocatalytic $CO_2$ conversion to useful fuels is widely studied to enhance the activity and selectivity of the $CO_2$ photoreduction reactions. In this review, an overview of fundamental aspects of the $CO_2$ reduction photocatalysts is provided. The recent development of the photocatalyst is also discussed, focusing on the mechanisms of light harvesting and charge transfer. Besides, this review sets its sight on inspiring new ideas toward a practical $CO_2$ conversion technology.

We fabricated two different transparent conducting oxide thin films of ZnO doped with Ga ($Ga_2O_3$ 0.9 wt%) as well as Al ($Al_2O_3$ 2.1 wt%) (GAZO) and ZnO doped only with Al ($Al_2O_3$ 3 wt%) (AZO). It was investigated how it affects the moisture resistance of the transparent electrode. In addition, $Cu(In,Ga)Se_2$ thin film solar cells with two transparent oxides as front electrodes were fabricated, and the correlation between humidity resistance of transparent electrodes and device performance of solar cells was examined. When both transparent electrodes were exposed to high temperature distilled water, they showed a rapid increase in sheet resistance and a decrease in the fill factor of the solar cell. However, AZO showed a drastic decrease in efficiency at the beginning of exposure, while GAZO showed that the deterioration of efficiency occurred over a long period of time and that the long term moisture resistance of GAZO was better.

$CuSbS_2$ (CAS) and $CuSbSe_2$ (CASe) nanocrystals (NCs), which consist of earth-abundant elements, were synthesized by a mechanochemical method. Elemental precursors such as copper, antimony, sulfur, and selenium were used without adding any organic solvents or additives. The NCs were synthesized by milling for a few hours. The sudden phase changes occurred by self-ignition and propagation, as previously observed in other mechanochemical synthetic processes. The XRD, Raman, and TEM analysis were carried out to determine the crystallinity and secondary phase of the as-synthesized CAS and CASe NCs, confirming the phase-pure synthesis of CAS and CASe. Optical properties were investigated by UV-Vis spectroscopy and it was observed that the band gap energies were about 1.1 and 1.5 eV, respectively for CAS and CASe, suggesting the potential for the use as solar cell materials. The NC colloids dispersed in anhydrous ethanol were prepared and coated on Mo substrates by a facile doctor-blade method. The investigation on the solar cell properties of the as-synthesized materials is underway.

Transition metal dichalcogenides (TMDs) have attracted much attention because of their excellent optical and electrical properties, which are the applications of next generation photoelectric devices. In this study, $MoS_2$, which is a representative material of TMDs, was formed by magnetic sputtering method and surface changes and optical characteristics were changed with thickness variation. In addition, by implementing the photodetector of $MoS_2/p-Si$ structure, it was confirmed that the change of the electrical properties rather than the change of the optical properties according to the thickness change of $MoS_2$ affects the photoresponse ratio of the photodetector. This result can be used to fabricate effective photoelectric devices using $MoS_2$.