能隙工程於銅銦鎵硒薄膜製程暨太陽能特性之應用研究

Abstract

本論文研究銅銦鎵硒（CIGSe）吸收層之能隙調變工程於薄膜太陽能產業應用。能隙分佈曲線對於太陽能電池效率有重大影響。在傳統兩階段硒化製程中，元素擴散、硒化不完全、或二次相分離等因素導致吸收層之能隙分佈不佳而大幅降低電池效率，傳統硒化更使用毒性氫化硒（H2Se）反應氣體來提升吸收層薄膜品質。本研究以無毒元素硒作為硒化反應物取代H2Se來提升製程與環境安全性，並提出優化後的製程來補償無毒硒化的效應。另外，本研究首先針對CIGSe薄膜特性於硒化環境之硒元素含量進行探討並初步優化其結晶品質，並提出預熱處理來減緩元素擴散與二次相分離並提升晶相與能隙分佈均勻性。再者本研究更提出鎵元素擴散法來進行CIGSe吸收層之能隙調變工程，結合上述實驗成果後，成功製作高緻密度、單一晶相、且具備雙斜率能隙曲線分佈之CIGSe吸收層薄膜。本研究成功探討了CIGSe結晶薄膜製程之物理機制，提高元件轉換效率，並能促進薄膜太陽能應用之可能性。

This dissertation aims to develop an improvement of the Cu(In1-XGaX)Se2 (CIGSe) solar technology by bandgap modulation engineering based on modified selenization manufacturing. The bandgap values exhibit dominant effects on electrical performances. Several issues that bring about inadequate band distribution of CIGSe are suspended for year, such as elementary diffusion, incomplete selenization of phase segregation, toxic reactant materials, etc. Furthermore, to satisfy the environment-safe issue, the toxic reactant (H2Se gas) extensively used in selenization process was replaced by elemental selenium vapors in this work. We investigated the effect of selenium environment during the selenization procedure on the CIGSe crystallinity. A pre-heating treatment (PHT) is proposed to suppress the inhomogeneous and segregated phases by incorporating selenium elements into the precursors. Afterwards, we proposed a post gallium diffusion (PGD) process to adjust the band structure of CIGSe films. The CIGSe thin film has been demonstrated with pure chalcopyrite phase, well-crystallized morphology, and in-depth double-graded bandgap distribution through the film. This work explored the physics of crystalline CIGSe thin-film deposition to increase solar efficiency and the potentiality for improving thin-film solar applications.