Kwang Mook Park

Fabrication and Characteristics of mc-Si Solar Cells with RIE-Textured Surface

Reactive ion etching (RIE) texturing is well-known as an effective method to form the surface structure on a multi-crystalline (mc-Si) wafer that has grains with randomly oriented crystallites. The saw damage removal (SDR) process using HF/HNO3/D.I (HND) solution was employed in this work, since the etching rate of RIE dry etching was lower than that of wet etching. The surface morphology on mc-Si surface was formed by RIE using a gas flow ratio of SF6:O2 = 1:1.22. The control of RF power and working pressure could etch the mc-Si surface of the 15.6 × 15.6 cm2 area uniformly during RIE texturing process. The surface morphologies textured for 5 and 10 min were needle-like structures and sharp grass-like structures, respectively. Solar cells with the needle-like structure had higher values for open circuit voltage (Voc), short circuit current (Isc), fill factor (FF), and efficiency, despite higher reflectance compared to those with the sharp grass-like structure. The cell textured for 10 min was expected to have non-homogeneous emitter layer as the dark I-V curves of the cells textured for 5 and 10 min were compared.

Study of the p-i-n Layer to Enhance a-Si:H Solar Cell Efficiency Based on Single Junction

We investigated the optimum thickness of the p-, i-, and n-layers to improve transmittance of the p-layer, the absorbance of the i-layer and the recombination rate of the n-layer. a-Si:H-based solar cells with different thicknesses for each layer were fabricated using plasma enhanced chemical vapor deposition (PECVD) and their performance parameters were compared. The optical properties of the intrinsic layer (i-layer) and the optimum hydrogen content in the i-layer were investigated and analyzed using UV/Vis/NIR and FT-IR, respectively. The optimum thicknesses of the p-, the i-, and the n-layer represented about 300, 2000, and 600 Å, respectively. The maximum absorbance and the minimum transmittance were measured at an i-layer thickness of 2000 Å in the wavelength range between 400 and 800 nm. The FT-IR measurements showed the optimum hydrogen content in the i-layer was about 10.1 at.%. We verified that the thickness of each layer and the hydrogen content had greatly influenced the electrical properties of the fabricated cells.

Characteristics of a-SiC:H/a-SiGe:H/a-Si:H Thin Film Solar Cells Enhanced by CH4 Flow Rates Controlling in P-Layer

We fabricated a a-SiC:H / a-SiGe:H / a-Si:H thin film solar cell by adjusting CH4 flow rate in order to absorb long wavelength of solar spectrum without stacked structures such as triple junctions. The a-SiC:H, a-SiGe:H and a-Si:H layers with sheet resistance 7∼8 ohm/sq were deposited on indium tin oxide (ITO) glass by 13.56 MHz radical-assisted plasma-enhanced chemical vapor deposition (RA-PECVD). The working pressure and substrate temperature were 750 mTorr and 250°C, respectively. The a-SiC:H films for p-layer thickness of 300 Å were deposited using 10% CH4 diluted in H2. The thickness of a-SiGe:H for i-layer corresponded to 2000 Å. The n-layer was fabricated using 1% PH3 in diluted H2. The optical properties of these films were measured by UV-VIS spectrophotometer. The thickness of the film was estimated by FE-SEM were observation. The various values of Jsc, Voc, FF and conversion efficiency were evaluated by the solar simulator.