Potassium Postdeposition Treatment-Induced Band Gap Widening at Cu(In,Ga)Se2 Surfaces 鈥?Reason for Performance Leap?

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• 作者：Evelyn Handick ; Patrick Reinhard ; Jan-Hendrik Alsmeier ; Leonard K枚hler ; Fabian Pianezzi ; Stefan Krause ; Mihaela Gorgoi ; Eiji Ikenaga ; Norbert Koch ; Regan G. Wilks ; Stephan Buecheler ; Ayodhya N. Tiwari ; Marcus B盲r
• 刊名：ACS Applied Materials & Interfaces
• 出版年：2015
• 出版时间：December 16, 2015
• 年：2015
• 卷：7
• 期：49
• 页码：27414-27420
• 全文大小：325K
• ISSN：1944-8252

文摘

Direct and inverse photoemission were used to study the impact of alkali fluoride postdeposition treatments on the chemical and electronic surface structure of Cu(In,Ga)Se₂ (CIGSe) thin films used for high-efficiency flexible solar cells. We find a large surface band gap (E_g^Surf, up to 2.52 eV) for a NaF/KF-postdeposition treated (PDT) absorber significantly increases compared to the CIGSe bulk band gap and to the E_g^Surf of 1.61 eV found for an absorber treated with NaF only. Both the valence band maximum (VBM) and the conduction band minimum shift away from the Fermi level. Depth-dependent photoemission measurements reveal that the VBM decreases with increasing surface sensitivity for both samples; this effect is more pronounced for the NaF/KF-PDT CIGSe sample. The observed electronic structure changes can be linked to the recent breakthroughs in CIGSe device efficiencies.