Preparation And Characterization Of The CIGS Thin Films With Double-Graded Band GAP

Copper indium gallium selenide (CIGS) thin film solar cell is one of the most promising solar cells for its strong radiation resistance, high conversion efficiency, stable performance, etc. The absorbing layer of CIGS thin film solar cells with high conversion efficiency usually have graded band gap, which can be adjusted by changing Ga/(Ga+In) ratio in the films. In this thesis, CIGS absorber layer with different Ga/(Ga+In) ratio were prepared by pulsed laser sputtering CIGS quaternary target and subsequently annealing process.The structure, morphology, composition and optical band gap of CIGS thin films with different Ga/(Ga+In) ratio were studied. The results shows that high crystallinity CIGS films with smooth surface can be prepared by pulsed laser deposition (PLD). With the heat treatment temperature increasing, the grain size increases gradually, the intensity of (112) diffraction peak increases and subsequently decreases. The preferential orientation is along (112) direction. With the increase of Ga content in the film,(112) diffraction peak of CIGS film shifts toward right and the interplanar spacing decreases. The influence of different Ga contents on band gap was studied, the optical band gap of the CIGS thin films increases with an increase of Ga contents.In order to preparing graded band gap CIGS films, CIGS films with different Ga content were sequentially deposited on the same soda lime glass to adjust the Ga/(Ga+In) ratio of the films. The Ga/(Ga+In) ratio increases and subsequently decreases in the depth direction. The thickness of prepared CIGS film were controlled by sputtering energy and counts. The elements of thin film were studied with XPS etched layer-by-layer, variation of band gap in the depth direction was calculated by the band gap approximate formula. The double-graded band gap thin films with excellent structural, optical and electrical properties were eventually obtained.