自從J. Wu等人在2002年發現了氮化銦(InN)的真實能隙大小約為0.7電子伏特(~0.7 eV)，三族氮化物(III-Nitrides)便成了熱門的太陽能電池材料，因為氮化銦鎵(InGaN)化合物的能隙範圍在0.7 eV到3.4 eV之間，幾乎涵蓋了太陽光譜全部的波長範圍。儘管許多研究都指出含漸變銦含量的太陽能電池具有優秀的性能表現，但多數為模擬或理論的結果，含漸變銦含量主動層的氮化銦鎵太陽能電池的潛力需要經由實驗結果的證明。 在我們的研究當中，我們製備的樣品有:氮化鎵/氮化銦鎵多重量子井太陽能電池、氮化鎵/氮化銦鎵p-i-n太陽能電池，以及含漸變銦含量主動層的氮化銦鎵太陽能電池。所有元件皆以有機金屬化學氣相沉積法(MOCVD)生長於藍寶石(sapphire)基板上，並且透過光致發光、在AM1.5G太陽光模擬器下的電流-電壓太陽能電池特性曲線、外部量子效率以及X光繞等方法分析。雖然銦含量漸變的主動層有比較高的填充因子，該元件的轉換效率卻低於含量子井主動層的太陽能電池。除了氮化銦鎵的磊晶層品質應提升外，消除氮化鎵和氮化銦鎵之間的能帶斷層(band offest)也可能提升光載子的收集，因而增加元件的轉換效率。 ;III-Nitrides have become the potential material for solar cells (SCs) since the true band gap of InN (~0.7 eV) was discovered by J. Wu et al. in 2002. The band gap of the InGaN can be varied from 0.7 eV to 3.4 eV, covering nearly the full solar spectrum. Although many theoretical studies indicate that graded InGaN junctions exhibit great potential for high-efficiency SCs, the photovoltaic performances of graded InGaN junctions have not been studied to date. In this project, III-nitride SCs with three types of active region were fabricated: InGaN/GaN multiple quantum wells (MQW), the unintentionally doped InGaN single junction, and the InGaN junction with step-graded indium composition. All the samples were grown by metal organic chemical vapor deposition (MOCVD). Material/device characterizations were performed with photoluminescence (PL), X-ray diffraction, I-V curves under solar illumination, and external quantum efficiency (EQE). It is found that the device with graded junction, despite her larger fill factor, exhibits lower conversion efficiency than the one with MQW structure. The results were attributed to the inferior crystal qualities with the composition-graded junction. Carrier collection efficiency (and thus conversion efficiency) of the graded junction can also be improved by eliminating the band offset at the InGaN/n-GaN interface.
