P-layer properties on the performance of a-Si:H p-i-n solar cells

• Main Authors: Yo-Jin Yang, 楊侑縉
• Other Authors: 江雨龍
• Format: Others
• Language: zh-TW
• Published: 2014
• Online Access: http://ndltd.ncl.edu.tw/handle/96085935900787486094

碩士 === 國立中興大學 === 光電工程研究所 === 102 === The window layer of hydrogenated amorphous silicon (a-Si:H) p-i-n thin-film solar cell is p-layer, which affects the number of photons that incident into the absorber i-layer. It forms the pn junction and TCO/p junction, which causes the variation of the built-in electric field and the series resistance. In this thesis, various p-layers of a-Si:H p-i-n solar cells were fabricated to investigate the effects of the bandgap (Eg), the activation energy (Ea) of p-layer and the double p-layers structure on the performance of solar cells. There were three designs to produce the window p-layer (a-SiCx:H:By) by (1) modulation the methane gas flow ratio (Cx) to change Eg of p-layers, and to study their effects on solar cells, (2) modulation the methane and diborane gas flow ratio {Cx(By)} to obtain the p-layers with the same Eg but change their Ea, and to explore the effects of Ea on solar cells, (3) combination a high Eg p-layer (PH) and a low Eg p-layer (PL) to form a double Eg p-layers, and to investigate the effects of (a) PL/PH and PH/PL, (b) fixing the total thickness of PL/PH and modulating the thickness of PL, and (c) fixing the thickness ratio of PL/PH and modulating its total thickness on the performance of solar cells. In the design (1), increasing Cx could raise the Eg of p-layers, resulting in the decrease of the light absorption in the window layer, and generating more electron-hole pairs in i-layer. The open-circuit voltage (Voc) and the short-circuit current density (Jsc) were increased. However, high bandgap offset at the p/i interface and high energy barrier at the TCO/p interface increased the series resistance (Rs), and reduced the fill factor (FF). In the design (2), modulation {Cx(By)} to produce the p-layers of same Eg with different Ea, high Ea increased the Rs,resulting in the decrease of FF. In the design (3), the double p-layers structure of (a) PL/PH and PH/PL, adding the low-Eg PL between the TCO and the high-Eg PH increased conductivity and reduced Rs, resulting in the increase of FF and the efficiency (η) of solar cells. Adding the low-Eg PL between the high-Eg PH and i-layer reduced the band offset, resulting in slightly increase of FF, but significantly decrease of Voc and ?? In the design (3), the double p-layers structure of (b) fixing the total thickness of PL/PH and modulating the thickness of PL, increasing the PL thickness reduced Rs, resulting in the increase of FF, but the decrease of Voc and Jsc. The maximum Voc was obtained for the PL_50% solar cell. The appropriate PL thickness ratio of PL/PH double p-layers could improve the efficiency of solar cell. In the design (3), the double p-layers structure of (c) fixing the thickness ratio of PL/PH and modulating its total thickness, reducing the PL/PH total thickness could make more photons penetration into i-layer, and let the hole carries easily tunneling through the p-layer, resulting in the increase of Jsc, FF and η. Thin PL/PH total thickness could improve the efficiency of solar cell. In this thesis, the highest efficiency solar cell was fabricated by a double p-layers structure with thin PL/PH total thickness, the η, Jsc, Voc, and FF were 7.12%, 12.66 mA/cm2, 0.802 V and 70%, respectively.