利用時間解析光激發-探測光譜研究不同轉換效率銅銦鎵硒薄膜之超快載子動力學

Abstract

本碩論藉由研究不同轉換效率銅銦鎵硒薄膜的材料特性與超快載子動力學，來找出與太陽能電池轉換效率最相關的訊息。我們發現在高轉換效率的樣品，其I(220)/I(112)比例能同時能與n-layer硫化鎘晶格匹配且使鎘離子擴散至其中形成同質的pn接面減少漏電流。同時也發現高轉換效率的樣品存在銅缺少的特性，使表面粗糙度降低改善短路電流，除此之外，在高轉換效率的樣品中，鎵/銦+鎵的成份隨著縱深增加而增加，此濃度梯度變化使得光激發載子的收集率得以提升。而在超快載子動力學研究上，在高轉換效率樣品中的熱載子冷卻速率和缺陷復合速率遠低於其他樣品，分別是受到較多背景電子濃度以及較少界面缺陷的影響，希望透過此研究，能提供一更即時與直接的檢測方式，來提升太陽能電池的發展。

In this thesis, the material characteristics and ultrafast dynamics of different efficiency Cu(In,Ga)Se2 thin films are investigated. We found that I(220)/I(112) in high efficiency sample not only has better lattice match to n-layer CdS but also forms homogeneous pn junction to lower shunt leakage current. Also, Cu-poor characteristic exists in high efficiency sample that decreases surface roughness and increases photocurrent. The Ga/In+Ga doping profile is much obvious in high efficiency sample that enhances the collection of photoexcitation carrier. For ultrafast dynamics, the hot carrier cooling rate and defect-related recombination rate in high efficiency sample are much slower than other samples. The former is due to high background electron density and the later indicates that fewer interface defects in it. These results provide much faster and systematic study for realizing the relation between Cu(In,Ga)Se2 thin film quality and photovoltaic performance. We hope this study can optimize thin film deposition conditions and provide more useful information for improving efficiency.