本論文之主要目的在於利用模擬程式分析與設計分散式布拉格反射鏡之特性，並研究此反射鏡與單接面砷化鎵太陽能電池結合之特性，其太陽能電池藉由再次吸收分散式布拉格反射鏡所反射的光子，以提升輸出光電流及整體轉換效率。
利用傳遞矩陣法所建立的模擬程式能夠精確設計並預測分散式布拉格反射鏡之反射頻譜，使實驗測試的時間能夠有效地縮短。此外，此模擬程式也能夠模擬整體太陽能電池的反射頻譜，幫助我們分析具有分散式布拉格反射鏡之太陽能電池之外部量子效率在長波長波段有波動的增加情形產生。
利用有機金屬氣相沉積法製作砷化鎵太陽能電池，並於吸收層之後增加分散式布拉格反射鏡以反射尚未吸收的光，使太陽能電池再次吸收。藉由模擬及實驗調變不同反射頻譜，並利用高解析X 射線繞射儀與掃描式電子顯微鏡等量測設備分析磊晶層之成長速率，得到精確的磊晶層厚度。從實際量測可知，具有分散式布拉格反射鏡之砷化鎵太陽能電池可以有效地提升光電流從13.6 mA/cm2 到 15.0 mA/cm2。一般的分散式布拉格反射鏡的各層厚度約為70 nm，加上所選用的材料(砷化鎵及砷化鋁)具有較大的能帶差，因此光生載子在分散式布拉格反射鏡的再結合速率會增加，造成太陽能電池的漏電流增加，從10-7 A 增加到10-6 A，進而造成太陽能電池的效率無法有效提升。為了解決此問題，於是利用超晶格的結構來降低太陽能電池的漏電流。
由於超晶格分散式布拉格反射鏡具有較小的各層厚度，加上超晶格的連續能帶能使得載子不易再結合，且其反射頻譜可以藉由調整超晶格的週期數來改變中心波長，又其反射鏡之反射率與一般的反射鏡相當。因此使用超晶格分散式布拉格反射鏡仍然能讓太陽能電池的光電流增加，但不會增加太陽能電池的漏電流，所以具有超晶格分散式布拉格反射鏡太陽能電池的效率得以提升，從10.2% 增加到 10.7%。
最後，量測分散式布拉格反射鏡太陽能電池於聚光條件下，從實際量測可知，具有超晶格分散式布拉格反射鏡之砷化鎵太陽能電池可以較一般砷化鎵太陽能電池的提升光電流從614 mA/cm2 增加到 636 mA/cm2，增加了22 mA/cm2，在聚光倍率為43 的條件下。效率方面則從10.7%增加到11.3%，相對增加5.7%，在聚光倍率為7的條件下。這是因為藉由增強入射光強度，增加超晶格分散式布拉格反射鏡反射再吸收的光子量，使得太陽能電池之效率可以更為明顯的提升。

The main purpose of this thesis is to investigate and design the properties of distributed Bragg reflector (DBR) structures by simulation programs and investigate the properties of single junction GaAs solar cells with DBR structures. And the enhancement of output photocurrent and conversion efficiency of solar cells are caused by the DBR structures’ reflection of photon to let solar cells absorb again.
The simulation programs are successfully established by the transfer matrix methods. By this program, we can design and precisely predict the reflectance spectra of DBR and SL-DBR structures, resulting in saving time of experiment tests. Moreover, these programs can also simulate the whole structures of solar cells, helping us analysis the phenomenon of fluctuant increment of external quantum efficiency of solar cells in long wavelength region.
The structures of GaAs solar cells on GaAs substrates were grown by MOVPE, and we insert DBR structures into the bottom of absorption layer to reflect the incident light in long wavelength region to recycle. By simulation and experiment, we modulated the different reflectance spectra, and derived the growth rates of epitaxial layers by high resolution X-ray diffraction and scanning electron microscope (SEM) to obtain the precise thickness of the epitaxial layers.
From measurement results, the GaAs solar cells with DBR structures can enhance the photocurrent from 13.6 mA/cm2 to 15.0 mA/cm2. Because the thickness of each layer of typical DBR structures is about 70 nm and the chosen materials, GaAs and AlAs, have larger difference of bangap, the recombination rate of the carrier generated by absorbed photon would increase in the DBR structures. Leading to the leakage current of solar cells with DBR structures increase, from 10-7 A to 10-6 A; thus, the efficiency of solar cells with DBR structures couldn’t effectively increase. To solve this problem, we would use the superlattice-DBR (SL-DBR) structures too reduce the leakage current of solar cells.
Due to the thinner thickness of each layer of SL-DBR structures and the miniband of superlattice, the recombination rate of carrier would decrease. In addition, the reflectance spectrum could be modulated by the number of period of superlattice and the reflectance of high reflectance region is approach to the value of DBR structures. Therefore, the photocurrent of the solar cells with SL-DBR structures would be enhanced and, at the same time, the leakage current of them would not increase, leading to increase the efficiency of solar cells with SL-DBR structure, from 10.2% to 10.7%.
Finally, the performance of the solar cells without and with DBR structures under concentration condition will be discussed. From the measurement results, the photocurrent of solar cells with SL-DBR structures is enhanced from 614 mA/cm2 to 636 mA/cm2, increased by 22 mA/cm2, under 43-sun condition. As to the efficiency of the solar cells with SL-DBR structures, it is enhanced from 10.7% to 11.3%, relatively increasing by 5.7%, under 7-sun condition. These are because the enhancement of incident light increases the amount of light reflected from SL-DBR structures, leading the efficiency of the solar cells with SL-DBR structures would increase.

Chapter 1

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Chapter 2

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Chapter 4

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Chapter 5

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Chapter 6

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