III-V族多接面太陽能電池之特性研究

The Characteristic Investigation of III-V Multijunction Solar Cells

傅毅耕(In-Keng Fu)

指導教授 ： 溫武義

中原大學/工學院/電子工程研究所/碩士(2006年)

https://doi.org/10.6840/cycu200600491

摘要

本實驗主要是製作一系列聚光型太陽能電池，研究著重在於聚光條件下對於太陽能電池的影響，在聚光條件下，元件的溫度會隨著聚光倍率越高而上升，而傳統式的多接面太陽能電池皆採用串聯式的結構，因此高溫下操作對於任一個子電池的影響將是必須被考慮的。故在本論文實驗中，首先將著重在改變溫度情況下，對於三接面太陽能電池的各個子電池的電流-電壓和量子效率的影響作一系列的分析，此外，在不同溫度下的能隙紅位移現象也將在此討論，藉由此改變溫度的實驗來研究磷化銦鎵、砷化鎵和鍺的熱效應，實驗結果可發現磷化銦鎵的熱穩定性最佳，最適合作為太陽能電池的上層子電池，砷化鎵子電池的暗電流會受到溫度升高而上升，暗電流的上升將會造成量子效率下降，而熱穩定性最差的是鍺子電池，實驗結果可發現在80℃的量子效率低於5%左右，且鍺子電池更存在著非線性的量子效率現象，此現象造成量測鍺子電池必須附加偏壓才能量測出鍺子電池的量子效率。
另一方面，由於聚光時的輸入光功率增加使得太陽能電池輸出的電流會大幅度的提升，但是由於串聯式的結構使得輸出電流將會受限於限制子電池，若各個子電池相連接的穿隧接面無法承受高聚光倍率下所產生的高電流，將會大幅度地降低太陽能電池的轉換效率，在此實驗中，我們發現穿隧接面的退化使得太陽能電池的轉換效率在聚光倍率為44.14倍比沒聚光時候下降了6.22%，因此，太陽能電池的穿隧接面使用在聚光條件下，其所扮演的角色將更加重要，如何的設計使得穿隧接面可以承受~A/cm2電流密度，本實驗將透過能帶分析以及理論計算來設計穿隧接面，透過此設計我們將克服此轉換效率下降的問題並且使得聚光實驗得以繼續進行下去。
當穿隧接面設計改良完之後，高聚光倍率的需求已經可以達到，而在完整的聚光量測過程中，除了聚光的效應影響著太陽能電池，其環境溫度本身對於太陽能電池的影響也必須考量，溫度以及聚光倍率在太陽能電池中到底扮演著什麼樣的角色，哪一個對於太陽能電池扮演著退化或幫助的角色，我們將透過一系列的實驗找出溫度和聚光倍率的影響，實驗結果將可發現溫度造成太陽能電池的轉換效率下降程度遠大於聚光倍率所能提升的程度，因此，溫度是影響太陽能電池最主要的因素。

關鍵字

太陽能電池 ； 穿隧接面效應 ； 聚光效應 ； 聚光型 ； 溫度效應

並列摘要

The object of this study is to analyze the characteristics of a series interconnected InGaP/GaAs/Ge concentrator solar cells. As is known, under concentrated-light operation condition, the device temperature arises with increasing light concentration ratio. Since subcells in a tandem structure are in series connection, the effect of temperature on any one of those subcells can affect the performance of the whole cell. The purpose of this work is to study the temperature effect on the spectral response and I-V characteristics of the tandem solar cells. We evaluated the temperature characteristics of individual subcells of InGaP/GaAs/Ge triple junction (3J) solar cell. In addition, the redshift of spectral responses at various temperatures is discussed in this study. We also investigated how the temperature influences the conversion efficiency of solar cells. Experimental results indicate that the thermal stability of InGaP subcell is better than the subcells of GaAs and Ge. InGaP subcell is most suitable to be used as the top subcell. The dark current of GaAs subcell arises with increasing temperature, which will cause the quantum efficiency to decrease. The thermal stability of Ge is the worst. Experimental results show that the quantum efficiency of Ge subcell is smaller than 5% at 80℃. Moreover, the Ge subcell has a non-linear phenomenon in quantum efficiency. One must add the voltage bias to suppress this phenomenon which is an unable factor for measuring the quantum efficiency of Ge subcell.
On the other hand, an improvement in the output current of solar cell is demonstrated due to an increase in the input power under concentrated-light conditions. However, the series structure causes the output current to be determined by a limitative subcell. If the tunnel junction which connects every two subcells can not bear the current caused by a high concentrated-light ratio, the conversion efficiency of solar cell will reduce substantially. In our experiments, the conversion efficiency of solar cell was seriously decreased by 6.22% at 44.14 suns compared with that at 1 sun due to the degeneracy of tunnel junction. Therefore, for such a high current density approaching tens of A/cm2, the tunnel junction connecting both the top and the bottom cells plays a critical role. How to design a tunnel junction that can bear a high current is the focus of our study. An optimal tunnel junction will be designed through the theoretical calculation and energy-band analysis in our study. Based on this design, we may overcome the lowering of conversion efficiency and make our experiments possible to be continued.
Once the improvement of the tunnel junction design is satisfactory, the requirement of high concentrated-light ratio can be met. Besides, to carry out a complete measurement on solar cell under a concentrated-light condition, the resultant effects caused by a rise in the surrounding temperature must also be considered except the concentrated-light effect itself. A series of experiments were performed to study the effects of temperature and concentrated-light ratio. Experimental results exhibit that the degree of decline in conversion efficiency of solar cell resulting from an increase in temperature is greater than that of rise caused by the concentrated-light effect. It is found from the present study that temperature is a important factor which influences seriously the performance of solar cells particularly under a concentrated-light operation condition.

並列關鍵字

temperature effect ； tunnel junction effect ； Concentrator ； Solar Cell ； InGaP/GaAs/Ge ； Concentration effect

參考文獻

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