非晶矽基光伏元件應用於環境光能量採集之研究

Abstract

使用非晶矽薄膜(a-Si:H)製作太陽能電池有一定優勢，包含低成本，薄膜光吸收隙數較高及低溫製程。另外非晶矽電池的頻譜響應和室內環境光源的輻射分布相符，電池也擁有高開路電壓(Voc)，可提供電路更高的操作電壓。因此非晶矽電池用於室內發電是有潛力的，可應用於互聯網IoT作為能量採集器。本研究製作p型非晶矽碳窗口層(p-a-SiC:H window layer)，以漸變能隙雙層非晶矽碳結構和銀背反射層用於非晶矽太陽能電池，在最佳條件下得到電池效率9.2 %。另外，製作非晶矽鍺薄膜(a-SiGe:H)，以FTIR、Bias-QE、及DLCP分析電漿功率(RF power)和氫氣流量對薄膜及電池影響，使用非晶矽緩衝層(buffer layer)增加電池表現。本研究亦製作a-Si:H/a-Si:H疊層電池。藉由電流匹配(current matching)、降低n/p junction阻值、及兩層a-SiC:H window layer優化電池，得到效率8.3 % 疊層電池。最後用螢光燈管模擬室內環境光，將本實驗製作的電池於不同環境光下量測I-V特性。電池頻譜響應是否匹配燈源會影響電池表現，相對於低色溫(3000K)螢光燈管，高色溫(6500K)螢光燈管下電池輸出功率較高。目前在弱光下效率的計算沒有一致的標準，不同效率的定義皆有探討。和其他電池相比。在不同光源下使用漸變能隙雙層非晶矽碳結構和銀背反射層之電池皆得到最高的效率。a-Si:H/a-Si:H疊層電池在低照度下(600 lux)下Voc仍大於1.2 V，此結果顯示電池在室內光提供高電壓驅動電路的可行性。

Fabricating solar cells using amorphous silicon (a-Si:H) has several advantages, including low cost, high light absorption coefficient, and low temperature deposition process. Besides, frequency response of a-Si:H cells matches indoor ambient light. High open current voltage (Voc) of a-Si:H cell provides high operation voltage for a circuit. Thus, a-Si:H cell has potential to be used for indoor energy harvesting. The cell can be applied to “Internet of Things” as an energy harvesting device. In this study, p-a-SiC:H is used as window layer. With two layer graded p-a-SiC:H structure and silver back reflector, we obtained high cell efficiency of 9.2 %. In addition, amorphous silicon germanium film (a-SiGe:H) was made. FTIR, Bias-QE and DLCP were used to examine the effect of RF power and hydrogen flow rate. a-Si:H buffer layer improves cell performance. In addition, a-Si:H/a-Si:H tandem cell was optimized by current matching, low resistivity n/p junction, and two layer graded a-SiC:H window layer. We obtained high efficiency of 8.3 % for tandem cell. Finally, commercial fluorescent tube was used to simulate indoor ambient light, and I-V characteristics of different cells were measured. Whether the frequency response of a cell matches the light source is important in ambient light illumination. Output power density of a cell is increased with 6500K fluorescent tube, compared with 3000K fluorescent tube. So far, there is no standard of efficiency calculation in weak light calculation. Different definition of efficiency is discussed. The a-Si:H cell with two layer graded window layer plus Ag back reflector has highest efficiency compared with other cells under different illumination condition. The Voc of a-Si:H/a-Si:H tandem cell is larger than 1.2 V in low irradiance (600 lux) illumination. This shows the possibility of high voltage to drive a circuit.