- 學位論文
單接面太陽能電池本質層厚度改變的光電特性
Optoelectronic Properties of i-Layer Thickness Dependence Single Junction Solar Cells
摘要
本論文主要研究p-i-n結構砷化鎵太陽電池的光電特性，藉由改變本質層(i-layer)厚度，量測出最佳轉換效率的太陽電池結構。照光下電壓-電流的量測結果顯示，本質層厚度為1nm的樣品之轉換效率，優於沒有本質層結構的樣品，可達最高的效率14.24％。 接著利用光激螢光以及時間解析光譜，進一步得到不同本質層厚度時之侷限深度(localization depth)與輻射載子生命期(radiative lifetime)。實驗結果顯示，在1 nm本質層中有最佳侷限深度在9.8 meV和輻射載子生命期5.3 ns。產生侷限效應的原因是由於鋅擴散至負型砷化鎵和本質層。因此以650℃進行退火、在不同時間模擬鋅擴散，發現退火時間愈長，侷限深度愈高、輻射載子生命期也隨之愈短。在ECV測量中，它清楚証實鋅的濃度是在回火後有顯著地變化。亦即鋅確實擴散至負型砷化鎵和本質層。 此外進一步量測各個樣品光激螢光的變化來討論由缺陷所引起的表面複合速率(surface recombination velocity)，也發現在本質層結構為1 nm太陽能電池的表面複合速率有明顯的改善。綜合實驗結果顯示在太陽能電池上適當地增加本質層厚度是有助於提高轉換效率。
並列摘要
In this thesis, we reported the optoelectronic characteristics of p-i-n GaAs solar cells. We studied the optimum thickness of intrinsic layer for obtaining the highest conversion efficiency. The samples without were detected by current-voltage measurement under AM1.5G illumination that the sample with 1 nm intrinsic layer has the highest efficiency of 14.24％. Based on low temperature photoluminescence and time resolved photoluminescence measurement, localization depth in such intrinsic layer thickness was developed. The experimental result showed that both localization depth (Eloc) at 9.8 meV and radiative lifetime (τrad) at 5.3 ns were achieved the best optoelectronic performance in 1 nm intrinsic layer. It was found out that the localization formed due to Zn diffusion in n-GaAs and intrinsic layer. Different samples annealed at 650℃ with different annealing time were attained to obtain the localization depth. It was clearly revealed that the longer annealed time, leads to the deeper localization, and to the shorter life time. The ECV measurements manifest that the Zn concentrations are changed dramatically. The evidence shows clearly that the Zn presented nominally in the lower n-GaAs and i-GaAs layer, as the result of diffusion. Furthermore, it was proposed to distinguish the front surface recombination velocity from the induced defects by variation the PL intensity. From this photoluminescence measurement, the surface recombination velocity of the solar cells with the intrinsic layer 1 nm is obviously improved. As these results, the thickness of intrinsic layer indeed deeply influences the efficiency of solar cell.