| 摘要: | 近幾年來，各種物理特性對矽基太陽能電池所產生的影響引起廣泛的研究，其中磊晶矽太陽能電池與異質接面太陽能電池均具有能在低溫下被製作，低成本且高效率之優點。磊晶矽太陽能電池可在很薄的射極層下，具有高摻雜之效果，也由於磊晶的關係，使得短路電流可以達到與傳統矽基太陽能電池一般之水平，相較之下，雖然異質接面太陽能電池之射極層為高吸收係數材料，導致短路電流較低，但由於射極層為高能隙之材料，可使異質接面太陽能電池擁有高開路電壓之優點。因此，我們將針對短路電流的部分作為改善的目標，其採取的方法為將射極層之材料替換為高能隙且低吸收係數材料，非晶碳化矽(a-SiC)，而後，利用鍺(Germanium)吸收近紅外光之特性，將矽鍺(Si1-xGex)材料加入當吸收層之一部分，以提高短路電流。在本論文中，我們將利用二維模擬軟體Synopsys TCAD集中於探討各種不同結構參數對於磊晶矽太陽能電池與異質接面太陽能電池在光電特性上之影響。
首先，我們建立一磊晶矽太陽能電池，其結構為ITO/ emitter (p+)/ base (n)/ BSF (n+)/ Ti/Ag，並針對各種不同參數作特性表現探討，其中參數包含厚度、摻雜濃度、復合速率以及功函數。從研究結果可以發現，當emitter (p+)/ base (n)/ BSF (n+)厚度依序為10 nm/300 μm/50 nm，摻雜濃度為1×1021/1.6×1015/1×1021 (cm-3) 及base兩端之接面復合速率為102 cm/sec時，為磊晶矽太陽能電池最佳化後之結構參數，其效率可高達21.2 %。除此之外，從ITO的功函數對元件特性的關係結果中，我們可以作出以下結論：為了達到歐姆接觸且有較好的電性，與p型摻雜接觸時，ITO之功函數須大於所接觸之半導體功函數，換言之，與n型摻雜接觸時，ITO之功函數則須小於所接觸之半導體功函數。
第二部分，我們建立一異質接面太陽能電池，其結構為ITO/ a-SiC (p)/ a-SiC (i)/ c-Si (n)/ a-Si (n+)，並針對其厚度、摻雜濃度、缺陷能態密度以及能隙作為探討，根據模擬結果可以發現，當以a-SiC/c-Si的結構取代a-Si/c-Si時，短路電流可提升1.7 mA/cm2，而加入Si1-xGex作為吸收層時，當Ge含量為91 %，短路電流可高達46.23 mA/cm2。
Recently, the effects of physical properties on silicon-based solar cells have been extensively researched such as the epitaxial silicon solar cell and hetero-junction solar cell which have been produced at low temperatures, low cost and high efficiency. The high doping concentration of an emitter layer in the epitaxial silicon solar cell can be used to form an ultra-shallow junction to obtain a high short current density. For the hetero-junction solar cell, the absorption in a-Si:H will results the lower short current density than the conventional silicon solar cells. Therefore, we use the materials of a-SiC and germanium in the HIT solar cell to enhance the Jsc. In this thesis, we focus on the electrical performance of structural parameters and two-dimensional device modeling for epitaxial silicon solar cell and hetero-junction solar cell are carried out by using Synopsys Technology Computer Aided Design (TCAD) simulation program.
First, we study the performance an emitter (p+)/ base (n)/ BSF (n+) epitaxial silicon solar cell with various parameters, such as the thickness, the doping concentration, the surface recombination velocity, and the work function. The optimal efficiency of 21.2 % can be achieved with 10 nm/300 μm/50 nm, doping concentration of 1×1021/1.6×1015/1×1021 (cm-3) and, the surface recombination velocity of emitter/base and base/BSF are 102 cm/sec.
Nevertheless, from the results of the cells with different ITO work function to achieve ohmic contact, if ITO contacted with p-doped layer, the ITO work function need to lager than the work function of semiconductor. On the other hand, ITO contacted with n-doped layer, the ITO work function need to smaller than the work function of semiconductor.
Second, we demonstrate an a-SiC (p)/ a-SiC (i)/ c-Si (n)/ a-Si (n+) hetero-junction solar cell. We investigate the effect of the thickness, the doping concentration, density of state, and band gap on the performance of the solar cell. According to the simulation results, the structure of a-SiC/c-Si can improve the Jsc of 1.7 mA/cm2. Then, the Jsc can be improved to 46.23 mA/cm2 by using Si0.09Ge0.91 in the HIT solar cell to absorb infared of sunlight. |
