| 摘要: | 異質接面太陽能電池(HIT)相較傳統矽晶電池(Diffusion cells)有幾項優點: 低溫低耗能製程、較高的開路電壓(Voc)與較好的溫度特性。本研究以電子迴旋共振化學氣相沉積法(Electron Cyclotron Resonance Chemical Vapor Deposition, ECRCVD)搭配電漿輔助化學氣相沉積法(Plasma Enhanced Chemical Vapor Deposition, PECVD)互相結合，來成長異質接面矽晶太陽能電池所需的摻雜層及鈍化層，並探討太陽能電池在光電特性與轉換效率上的表現。ECRCVD具有高沉積速率、低工作壓力、低離子轟擊且無電極汙染等優點，因此本研究利用ECR製作硼摻雜層當作射極層(Emitter)。而PECVD具有低沉積速率且容易成長高品質的超薄鈍化膜(厚度~5nm)與磷摻雜薄膜，因此本研究藉由PECVD沉積優良的鈍化層和背表面電場(BSF)來研製異質矽晶太陽能電池的效率優化探討。
本研究分別對優化載子生命週期、氫化非晶矽薄膜厚度、單晶矽基板厚度、摻雜層厚度與不同金字塔基板的數項製程因子對太陽能電池之影響進行討論。首先是使用pi-ip、ni-in堆疊結構分析生命週期，及對開路電壓與效率之影響；而在異質接面矽晶太陽能電池方面，利用電池結構為 Ag/ITO/a-Si:H(p)/a-Si:H(i)/c-Si(n)/a-Si:H(i)/a-Si:H(n)/ITO/Ag 於n型平面矽晶基板上調變氫化非晶矽薄膜厚度為0~10 nm時，可於10 nm鈍化薄膜製作而成面積1×1 cm2之異質接面矽晶太陽能電池的開路電壓可達690 mV；另外在調變單晶矽基板厚度由180 μm至50 μm時，在50 μm之n型平面超薄矽晶基板，可有效地降低載子複合速率到6 cm/s，且可得到最佳光電轉換效率: 開路電壓651 mV、短路電流29.28 mA/cm2、填充因子65.40 %、轉換效率12.46 %，由於超薄基板亦可降低太陽能電池晶片成本，因此預期會是往後極力發展的目標之一；固定摻雜層厚度為20 nm時有較佳的效率，因為在電性表現較好、載子濃度足夠；最後則是以不同金字塔尺寸基板所製作的異質接面太陽能電池做相互比較並分析，在厚度為200 μm 之n型矽晶基板上具有金字塔顆粒大小為3~5 μm，製作而成的異質接面矽晶太陽能電池可得到最佳光電轉換效率: 開路電壓660 mV、短路電流36.71 mA/cm2、填充因子71.1 %、轉換效率17.2 %。
;Heterojunction with Intrinsic Thin layer (HIT) solar cells have some advantages about low temperature, low power, high open circuit voltage, and good temperature coefficient. They are better than Diffusion cells. In this study, ECRCVD was used for the deposition of high doping silicon thin films, and PECVD was used for the deposition of high doping silicon thin films and passivation layers. These thin films were deposited on single-crystalline silicon substrate to fabricate the silicon hetero-junction solar cells. The optical properties, electrical properties, and solar cell performance of hetero-junction solar cells were investigated. ECRCVD has advantage about high deposition, low working pressure, low ion bombardment, and no electrode contamination. The boron-doped layer was deposited by ECR as emitter in HIT solar cells. On the other hand, the high quality passivation layers and the back surface field of phosphorus-doped layer were deposited by PECVD to fabricate the silicon hetero-junction solar cells.
We will investigate the optimization of carrier lifetime, different passivation layer, different wafer thickness, different doping layer, and different texture wafers. First, we are going to improve Voc and investigate the carrier lifetime with the structure of pi-ip and ni-in. The structure of HIT solar cell is Ag/ITO/a-Si:H(p)/a-Si:H(i)/c-Si(n)/a-Si:H(i)/a-Si:H(n)/ITO /Ag. The characteristics of hetero-junction solar cell on n-type planar substrate with the 10 nm-thick passivation layer are shown as follow: Voc = 690 mV in the area of 1 cm2. Moreover, the different thickness of wafers varying from 180 μm to 50 μm were also investigated. For 50 μm-thick substrate, the characteristics of hetero-junction solar cell on n-type planar substrate were shown as follow: surface recombination rate: 6 cm/s, Voc = 651 mV, Jsc = 29.28 mA/cm2, F.F. = 65.40 %, Efficiency = 12.46 %. This result is outstanding, therefore we will continue to research the HIT solar cells with ultra-thin substrates in the future. In our study, using the 20 nm-thick doping layer as emitter can achieve good conversion efficiency. In the end, we modulate the different textured wafers for HIT solar cells. The characteristics of 200 μm-thick hetero-junction solar cell with the grain size around 3~5 μm on n-type textured substrate are shown as follow: Voc = 660 mV, Jsc = 36.7 mA/cm2, F.F. = 71.1 %, Efficiency = 17.2 %. |
