Effect of Post alkali doping on the structures and characteristics of TCO back contact/CIGS interface
- 주제(키워드) TCO back contact CIGS , Alkali PDT process
- 발행기관 고려대학교 대학원
- 지도교수 김동환
- 지도교수 정증현
- 발행년도 2020
- 학위수여년월 2020. 8
- 학위구분 석사
- 학과 대학원 신소재공학과
- 원문페이지 84 p
- UCI I804:11009-000000232068
- DOI 10.23186/korea.000000232068.11009.0001175
- 본문언어 영어
- 제출원본 000046048257
초록/요약
Recently, the necessity of solar cells with transparent back electrodes has emerged due to the reasons of light-transmitting solar cells, bifacial solar cells, and tandem structure solar cells. CIGS solar cells should be fabricated with high efficiency based on TCO back contact for the same reason. In this study, ITO/CIGS solar cells were studied. When ITO is used as a back contact, carrier blocking occurs due to Schottky barrier generated by low work function of ITO and GaOx secondary phase generated during CIGS deposition process. In this study, we studied the characteristics of ITO/CIGS interfaces according to post deposition treatment (PDT) process, which is well known for its high efficiency CIGS solar cells. PDT process is known to be effective in improving the junction characteristics with CdS buffer layer by forming Cu depletion layer on bulk property and CIGS surface of CIGS. However, this study also revealed that ITO (back contact)/CIGS interface has an effect. When NaF PDT was applied, the ohmic like contact could be realized by overcoming Schottky barrier on ITO/CIGS interface. This result suggests that deep level defects were generated when sufficient Na was doped on GaOx of thin thickness, resulting in carrier trap assisted tunneling. On the contrary, KF PDT failed to overcome the Schottky barrier of ITO/CIGS interface, which was analyzed by considering that the carrier tunneling probability decreased unlike the NaF PDT process. In fact, the decrease of carrier density was determined by CV measurement and the defect of ITO/CIGS interface was reduced by PL spectra. This result shows that the characteristics of ITO/CIGS interfaces change according to PDT process. To overcome this problem, we have conducted a study to create ohmic contact by applying Mo interlayer to ITO/CIGS interface. In the case of thick Mo, it was not possible to create a transparent back contact that was out of the original purpose, so a very thin Mo interlayer was applied. ITO/CIGS interface engineering was possible with Mo with a thickness of 0.5 nm, and as a result, ITO/CIGS solar cell with improved carrier blocking was produced.
more목차
1. Introduction 1
2. Theoretical background 9
2.1 Principle of solar cells 9
2.2 Solar Cell Efficiency Parameters 10
2.3 Cu(In,Ga)Se_2 solar cell 13
2.4 Post Deposition Treatment (PDT Process) 21
3. Experiment method 36
3.1 Fabrication of CIGS solar cell 36
3.2 Characterization 37
3.2.1 IV curve measurement 37
3.2.2 Temperature dependent Current-Voltage characteristics 38
3.2.3 Back-contact/CIGS interface barrier characteristics 38
3.2.4 Depth profile of elements of CIGS 39
3.2.5 Microstructure of CIGS solar cell 39
4. Results and Discussion 42
4.1 CIGS solar cell performance by Back contact condition 42
4.2 CIGS solar cell performance according to PDT process 44
4.3 ITO/CIGS interface Schottky barrier 47
4.4 Hole concentration in CIGS layer by PDT process 48
4.5 Back contact/CIGS interface Defect property 49
4.6 Back contact/CIGS Interface Microstructure 50
4.7 ITO/Mo interlayer/CIGS 52
5. Conclusion 68
