Band gap engineering of atomic layer deposited ZnxSn1‐xO buffer for efficient Cu(In, Ga)Se2 solar cell. (15th April 2018)

• Record Type: Journal Article
• Authors: Agbenyeke, Raphael Edem; Song, Soomin; Park, Bo Keun; Kim, Gun Hwan; Yun, Jae Ho; Chung, Taek‐Mo; Kim, Chang Gyoun; Han, Jeong Hwan
• Is Part Of: Progress in photovoltaics. Volume 26:Number 9(2018)
• Page Start: 745
• Page End: 751
• Publication Date: 2018-04-15
• Subjects: atomic layer deposition -- band gap bowing -- conduction band offset -- photo‐conversion efficiency -- Zn1‐xSnxO; Solar cells -- Periodicals; Photovoltaic cells -- Periodicals; Solar power plants -- Periodicals; 621.31245
• DOI: 10.1002/pip.3012
• Languages: English
• ISSNs: 1062-7995

Abstract

Abstract: Ternary zinc tin oxide (ZTO) is one of the few environmental compatible buffer materials with the potential of replacing the n ‐CdS buffer in Cu(In, Ga)Se2 (CIGS) solar cells and other photovoltaic systems once its properties are fully understood and optimized. In this work, ZTO films were grown by atomic layer deposition and were logically characterized with the aim of understanding the correlations between compositional changes and film properties. The ZnO:SnO2 pulse ratio significantly affected the growth rate, crystal structure, morphology, and band gap of the ZTO films. By controlling the Sn/(Sn + Zn) atomic ratio, the optical band gap of the ZTO films was tuned between 3.05 and 3.36 eV. Integrating the ZTO films as buffer layers in CIGS solar cells, we observed that films with Sn concentrations of 9 to 16 at.% yielded photo‐conversion efficiency close to 14%, which was very comparable to efficiency attained with the commonly used CdS buffer. Furthermore, using X‐ray photoelectron spectroscopy analysis, we correlated the current‐voltage behavior of the cells to the conduction band offset at the ZTO/ CIGS interface. Abstract : Careful modulation of the optical band gap of ternary Znx Sn1‐x O films via composition control in an ALD process paved way for their application as efficient buffer layers in CIGS solar cells. Films with Sn/(Sn + Zn) atomic percent between 9 and 16% resulted in an optimum spike type conduction band offset and efficient charge transport. The best cell achieved a conversion efficiency of 13.9%, which is very comparable to the 14.4% achieved by the CdS reference cell.