| Summary: | 碩士 === 南台科技大學 === 光電工程系 === 101 === Nano-porous silicon (NPS) possesses several advantageous characteristics for solar cell applications, including the light absorption spectrum close to the solar spectrum and low light-reflection coefficient from its effective textured structures. Unfortunately, the high resistivity of this material is apt to cause high series resistance of the device and results in poor conversion efficiency. In this thesis, trenched-electrode-contact (TEC) structures were added into design and fabrication of NPS surface layers of polycrystalline silicon solar cells, aiming to reduce the series resistance and enhance the optoelectronic conversion efficiency of the devices.
To prepare NPS layers, n+-type poly-Si surface layers were firstly formed on p-type (100) poly-Si wafers by an iterative-diffusion doping technique. Then NPS films were prepared on the heavily-doped n+-poly-Si layers by an anodic etching process, and the oxidized-NPS (ONPS) films were made from NPS by rapid-thermal-oxidation (RTO) treatments to stabilize the properties of NPS. Thereafter, inter-digitated trenched structures were formed on the ONPS layers by a RIE process. Finally, Cr/Al metal were deposited onto the trenches to construct the electrodes and to complete the device’s structure.
Experimental results from solar-simulator measurement showed that devices with TEC got photocurrent of 81.1 mA at a bias of 5V and short-circuit current of 11.77mA, that is about 4.2 times and 4.9 times respectively higher than those of devices without TEC. Especially, the TEC solar cell achieved conversion efficiency of 4.1%, which is about 8 times larger than that of a non-TEC cell. It was thought that trenched electrode contacts provide photocurrent flow routes that directly access the polysilicon substrates, instead of passing through the high resistive NPS layers. Therefore the short-circuit current and the conversion efficiency of the device increase, as a result of reduced devices’ series resistance.
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