以非晶矽鍺碳發展之薄膜堆疊型太陽能電池

Abstract

本論文之研究利用高密度電漿化學氣相沉積系統低溫、高解離率等優點製備低缺陷密度之氫化非晶矽薄膜，發展參雜鍺和碳之氫化非晶矽(a-Si, a-SiGe, a-SiC)調變能隙漸變之矽薄膜太陽能電池。由於氫化非晶矽薄膜能隙較高(1.8~1.9eV)，氫化非晶矽薄膜太陽能電池有高開路電壓的優點，但相對在太陽光譜中長波長的部分(750nm以上)無法有效吸收而造成短路電流密度較低。為了克服上述氫化非晶矽薄膜太陽能電池之缺點，我們開發非晶矽基能隙漸變薄膜a-SixGe1-x (1.4~1.6eV) 、SiyC1-y(1.9~2.0eV)，使其可吸收太陽光譜中不同波段的，有效的增強光伏特元件吸收寬頻太陽光能的利用率，並且可以以各種不同能隙所製備的矽薄膜太陽能電池為基礎發展多接面堆疊型太陽能電池，吸收可見光中各個不同波段的光，並且具有較高的開路電壓(2.0~2.3V)。本實驗室目前已經開發出各種不同能隙知單接面氫化非晶矽太陽能電池，其中單接面氫化非晶矽薄膜太陽能電池轉換效率達8.7%，矽鍺薄膜太陽能電池轉換效率約7%，碳化矽薄膜太陽能電池轉換效率也已經達到約8%的高效率成果，且從量子效率量測結果可看出和非晶矽太陽能電池相比矽鍺薄膜太陽能電池在700~850nm以及碳化矽薄膜太陽能電池在350~500nm皆有顯著的提升。而堆疊型太陽能電池的部分，我們目前已經開發了雙層和三層堆疊型太陽能電池，其中a-Si/a-Si以及a-Si/a-SiGe雙層堆疊型薄膜太陽能電池開路電壓分別可達到1.6以及1.4V，a-Si/a-Si/a-SiGe三層堆疊型太陽能電池開路電壓為2.07 V，目前已經可以將多個太陽能堆疊起來在電壓的表現有很好的串接效果，而a-Si/a-Si以及a-Si/a-SiGe雙層堆疊型薄膜太陽能電池轉換效率則分別為6.5%和5%，三層的堆疊型太陽能電池轉換效率3.5%，未來研究的方向將致力於改善堆疊型太陽能電池各接面間的穿隧接面，以提高堆疊型太陽能電池之短路電流進而提升轉換效率。

We have fabricated silicon-based alloy thin film solar cell by using high density plasma method. The high dissociation capacity of HDPCVD can be used to yield high-density plasma and markedly increased electron temperature, promoting the diffusion capability of the reactive radicals and eventually yielding low-defect a-Si films at low temperatures. Due to high optical band gap of amorphous silicon thin film, a-Si thin film solar cell shows the property of high open circuit voltage. But, this feature also limit the absorption in the near infrared part of solar spectra, so the short circuit current density is much lower compared with amorphous silicon germanium and microcrystal thin film silicon solar cell. In order to overcome the above-mentioned shortcomings, we utilize the amorphous silicon-based alloy, which are a-SixGe1-x (1.4~1.6eV) and SiyC1-y(1.9~2.0eV), to engineer the optical bandgap. The thin films with different optical bandgap could absorb the different part in solar spectra. Thus, we can effectively take advantage of the full solar spectra. And we can also develop muti-junction thin film solar cell based in the thin film solar cells. Each junctions of muti-junction solar cell have different optical bandgap, so they could absorb different part of solar spectra. Furthermore, the muti-junction solar cell has higher open voltage(2.0~2.3V). Currently, we have demonstrated single junction a-Si, a-SiGe and a-SiC thin film solar cell with conversion efficiency achieving 8.7%, 7% and 8%, respectively. Compared with a-si thin film solar cell, the quantum efficiency of a-SiGe and a-SiC significantly increased in 700~850nm and 350~500nm. Besides, we have also demonstrated double junctions solar cell, including a-Si/a-Si and a-Si/a-SiGe tandem solar cell and triple junction solar cell. The open circuit voltage of a-Si/a-Si, a-Si/a-SiGe tandem solar cells and a-Si/a-Si/a-SiGe triple junction solar cell is 1.6V, 1.4V and 2.07V respectively. The muti-junction we mentioned above have successful performance in open circuit voltage. Conversion efficiency of a-Si/a-Si , a-Si/a-SiGe and a-Si/a-Si/a-SiGe muti-junction solar cell tandem solar cell is 6.5%, 5% and 3.5% respectively. In the future, my research will focus on tunneling junction to reduce the recombination and upgrade short circuit performance.