氮化銦鎵/矽多接面堆疊太陽能電池數值模擬與結構最佳化

Abstract

本篇論文主要在於探討氮化銦鎵/矽多接面堆疊太陽能電池，為 了研究多接面堆疊太陽能電池，我們發展了一個等效穿隧層模型來 模擬多接面堆疊太陽能電池。當我們想計算多接面堆疊太陽能電池 的電流電壓曲線時，我們必須先計算出在高濃度的電子和電洞區的 電流穿隧的機率，然而在波松方程式，電流飄移擴散方程式以及連 續方程式中並沒有包含計算穿隧機率的式子。因此我們假設在高濃 度的電子電洞區之間有一層虛擬的等效穿隧層，藉由調整等效穿隧 層的能隙及輻射耦合係數我們可以用來解釋曲線能階對穿隧機率的 影響。 此外我們也提出電子電洞阻擋層對於光伏元件的影響，我們討論 了在單接面的太陽能電池中，電子電洞阻擋層對於太陽能電池效率 的影響。根據我們的研究結果，完美的電子電洞阻擋層的確有機會 提升太陽能電池的開路電壓和短路電流，因此我們從文獻中選取氧 化鎵及氧化鈦作為矽太陽能電池的電子電洞阻擋層，模擬的結果顯 示有了電子電洞阻擋層太陽能電池的開路電壓可以從0.65伏特提升 到0.80伏特，短路電流可以從35.1毫安培/平方公分提升到35.9毫安 培/平方公分，效率可以從21.9%提升到27.6%。 最後我們利用以上的方法，討論氮化銦鎵/矽多介面堆疊太陽能電池。我們找出在雙接面以及三接面最佳的音的比例以及各層的厚 度，我們也發現當我們以氮面生長漸變的氮化銦鎵層時，在異質接 面上的極化電荷可以幫助載子流出元件並且形成電子阻擋層，模擬 的結果顯示效率可以從29.6%提升到33.4%。

This thesis studied silicon based InxGa1−xN multi-junction tandem solar cells. To investigate the the multi-junction tandem solar cells, we developed a simulation model by using 1D Poisson and drift-diffusion solver with an assumed effective tunneling layer. As we know, if we want to calculate the current-voltage curve, we have to calculate the tunneling probability between the heavily doped n layer and p layer. However the 1D Poisson and drift-diffusion solver does not include the function to handle the tunneling current. Therefore, we assume that there is a virtual tunneling layer between the heavily doped n layer and p layer by changing the tunneling layer potential bandgap, recombination coefficient to explain influences of defect state level to the tunneling probability. Besides, we propose the concept of electron/hole blocking layer for the photovoltaic. We discusses the effect of electron/hole blocking layer on the photovoltaic performance of the single junction solar cells. The study shows that with a pure electron blocking on the p-type doping Si and a pure hole blocking layer on n-type doing, it is possible to enhance the open circuit voltage and short circuit current. Therefore, the Ga2O3 and TiO2 materials are chosen as the electron and hole blocking layer. The result shows that the open circuit voltage increases from 0.65 eV to 0.80 eV, and the short circuit current increases from 35.1 mA/cm2 to 35.9 mA/cm2 , where the power efficiency can increase from 21.9 % to 27.6 %. Finally, we use the above studies to investigate the performance of the silicon based InxGa1−xN multi-junction tandem solar cells. We find the optimized condition of the In composition and layer thickness of crystalline Si for the highest efficiency double-junction and triple-junction solar cells. After that, we analyzes the polarization effect on of the silicon based InxGa1−xN tandem junction solar cells with different top layer. Under the different InxGa1−xN growth face, the polarization charge at the heterojunction will induce different polarization field which can reduce or enhance the ability of the photo-generated holes collection. Making a great difference to the efficiency of the InxGa1−xN tandem junction solar cell. In our simulation, the graded InxGa1−xN tandem junction solar cells growth on the N-face can be the electron blocking layer which enhance the performance of the solar cells. The efficiency increases from 29.6% to 33.4%.