膠體量子點對於砷化鎵太陽能電池的影響及應用

Abstract

在本論文中，我們試著要把膠體銻化鎘量子點與砷化鎵太陽能電池結合起來，看能不能把太陽能電池的效率給提升。我們試了三種想法:第一種是把從公司買來得砷化鎵太陽能電池用銅膠貼在一個渡了金的玻片上，接著以太陽能電磁為中心隔出一個空間後再黏一層銅膠，然後再把混了HMDS(六甲基二矽氮烷)的量子點倒入剛形成的空間中，這樣的城牆設計是為了把量子點所發出的光能夠匯聚到太陽能電池上頭，但完成的元件量測完後並沒有顯示出效率增進的結果，這是因為量子點在城牆結構所圍出的空間中為沉於底部，以至於所發出的光沒辦法有效的匯聚在太陽能電池表面。 接著，第二種想法是我們試著在太陽能電池中去製作溝槽結構，從正面挖至接近P-N接面，接著把膠體銻化鎘量子點溶液倒入這樣的溝槽中，進而製造出LDS(Luminescent Down-Shifting)效應來增加我們的電池效率，然而，從EQE及增益因子可以看到說在短波長，LDS效應產生的增益勝過在長波長，AR(Anti-reflection)效應所產生的增益，雖然確實是有效率的增加但並不是很不明顯，這是由於在蝕刻這些溝槽時，會造成表面及接面的破壞，進而造成復合的增加及電流的流失。 為了改善溝槽所帶來的結構性破壞，第三種想法就是利用較厚的背面來製造溝槽結構，進而減少靠近接面的破壞。此方法必須要先把背面磨薄且拋光，然後才能進行後續的製程，因此我們會把砷化鎵黏在矽基板上，作為固定用，然而一開始我們是使用黏合機，以金屬對金屬的方式進行黏合，接著試著磨到大約50μm再進行後續製程，但很不幸地，完成的元件經測量後並沒有顯現二極體的曲線，反而是一條表現出電阻的斜直線，這是由於手磨上的困難導致在研磨時，N極的區域在元件的邊邊被磨光了。 接著我們試著不要磨那麼薄來避免N極區域被磨掉，大概控制在大約150μm左右，然後利用融化的銦球來黏在矽基板上。雖然以此製作出來的太陽能電池終於表現出了正常的二極體曲線，但卻沒有光伏效應的產生，這是因為元件太厚，距離P-N接面太遠，所產生的電子電洞沒辦法有效地到達接面反應產生光電流，在靠近表面的地方複合光了。

We try to combine the colloidal CdTe quantum dot and the single junction GaAs-based solar cell together in order to manage to make the performance of J-V characteristics of the GaAs –based solar cell mnch better. In this thesis, we introduce you three come-ups to manage to achieve our purpose to make J-V characteristics of the GaAs –based solar cell performing better. The come-up one is the design of wall structure, which construct the space to pour the CdTe quantum dot powder mixed with PDMS(Polydimethylsiloxane) into it and surround the normal GaAs-based solar cell to aim to concentrate the light illuminated from CdTe quantum dot on the surface of the solar cell, but the result seems not to be very effective. It is because that the CdTe quantum dot sink at the bottom so that the light can’t be concentrated on the surface of the solar cell. Then we try come-up two, the design of the trench structure from topside(p-region to n-region) which the colloidal CdTe QD can cast into it to bring the LDS effect closer to the p-n junction. The EQE and enhancement factor show the dominance of LDS effect in wavelength region while the AR effect prevails in longer wavelength region. The result really indicates the enhancement of JSC and efficiency but not very obviously because of possible trench depth and sidewall current leakage. Therefore, we try the come-up three, the design of the trench structure from backside(n-region to p-region). We think the n-region is enough thick to prevent possible trench depth and sidewall current leakage. There are two methods to lap and polish the backside of the GaAs wafer in advance and then do the continuing semiconductor process. The method one use bonding machine to bond the GaAs wafer on the silicon wafer in metal to metal and then manage to lap down to the thickness of about 50μm. Unfortunately, the J-V characteristics don’t show the normal performance of semiconductor because it is difficult to achieve the ideal flatness. Then we try the method two which doesn’t make the GaAs wafer so thin to prevent the n-region from totally lapping off, and stick it on the silicon wafer by melted In ball.Finally, the result shows the J-V characteristics of the normal performance of semiconductor, but it seems that there is no photovoltaic effect. Although these come-ups seem not very effective due to structural problems, we believe the combination between the quantum dot and GaAs-based solar cell can bring better performance of J-V characteristics if we can optimize the structural design.