利用下轉換機制提升太陽能電池效率

Abstract

近年來，轉換太陽光機制已有許多研究提出利用不同的材料與合成方法以提升其轉換太陽光之效率進而應用於太陽能電池之上，但由於新化合物的合成技術不穩定，造成其轉換效率低落，另一方面，轉換材料多半為有機物，與空氣接觸後會使得化合物內部的鍵解與空氣中的氧氣結合，進而使得響應不佳。在此，我們提出利用常見的釔鋁氧螢光粉( Y3Al5O12 )及矽酸鹽類螢光粉( (Ba, Sr)SiO4 )，此二類皆為氧化物，因此不需考慮隨著時間而造成轉換率下降及穩定性不佳的問題。作為下轉換層之材料，利用具下轉換機制之螢光粉末將未充分利用的高能量光子轉換成太陽能電池光譜響應較佳之低能光子。此方法克服電池在短波段的低頻譜響應與電池表面複合問題。實驗結果顯示，螢光粉噴塗至表面後，由於表面形貌造成全波段反射率下降外，另一方面也由於下轉換效應，使得紫外光能有效被利用，而不受到表面缺陷的影響，造成其轉換效率低落。在太陽能電池的電性不受影響之下，短路電流得到提升，進而增加了電池的效率。 本研究中，我們分析螢光粉下轉換層應用在砷化鎵電池表面的結果。實驗顯示，其短路電流有10~22%提升，電池的效率增加15~26%。進一步分析螢光粉在砷化鎵電池的螢光下轉換效率(螢光粉層吸光-放光後且在電池上產生電訊號的效率)，發現螢光粉在高劑量下會產生遮光現象影響了其入光量進而影響其效率。故我們在時實驗中亦有優化螢光粉之濃度，目的在找到其最佳濃度，使得下轉換與抗反射效應的消長之間能得到最佳數值，進而提升螢光下轉換層的效率。而最佳化之螢光粉劑量噴塗在太陽能電池上相較於傳統無螢光粉之砷化鎵太陽能電池可提高電流22.79%，而轉換效率高達25.27%。

Luminescent down-shifting (LDS) layers involve the conversion from underutilized high-energy photon to lower energy photon where the spectral response of the solar cell is more efficient. The method overcomes the poor response and surface recombination effect of solar cell at short wavelength. We apply the phosphor as luminescent down shifting layers in single junction GaAs solar cells to improve the ultraviolet light harvesting, surface reflection, and surface carrier collection properties and without limiting short circuit current. As a result, Jsc is increased, then increasing the power conversion efficiency (η) without electrical properties changing. Firstly, we examined YAG:Ce phosphor spraying on polydimethylsiloxane (PDMS) daubed on the surface of GaAs solar cells. As a result, the Jsc increased 10~20%, then increasing the η 15~25%. By analyzing the dosage of phosphor, we found that 3 milligrams has the best performance in JSC, because of the superposition of anti-reflection and LDS effect. However, there has a deep in 400nm, obviously in PLE. Instead of YAG:Ce, (Ba, Sr)SiO4, classified as silicate, are also used on solar cell. For the optimized dosage, the short circuit current density can up to 21.66 mA/cm2 and power conversion efficiency reaches to 16.51 % Finally, phosphor can apply in any kind of solar cells with increasing Jsc and η. This study shows the phosphors’ potential for becoming next generation solar cell in the future.