|タイトル||*平成25年度中間年報 太陽光発電システム次世代高性能技術の開発 フレキシブルＣＩＧＳ太陽電池モジュールの高効率化研究 （電子構造評価によるデバイス特性向上技術の開発）|
|報告書年度||2013 - 2013|
|英文要約||Title: The development of high performance flexible CIGS PV modules Development of key technologies for high-performance CIGS solar cells and modules based on characterization of their electronic structure (FY2010-FY2014) FY2013 Annual Report
1. Objectives: Electronic structures at interfaces and electronic activity of grain boundaries are to be investigated for developing key technologies for higher conversion efficiency in CIGS based flexible modules. Correlations between these characteristics and fabrication parameters and guiding principle for process-optimization are to be clarified.
2. For FY 2013 (1) Clarification of electronic structure of the CIGS layers grown on the flexible polymer substrate by three-stage evaporation
An introduction of the new polymer substrate in this financial year requires lower growth temperature of the CIGS. It is necessary to clarify the electronic structure of the CIGS grown under such conditions. The surface nature of the CIGS grown on the Mo-coated polymer substrates has been examined by means of PES/IPES and KPFM. The XPS results showed that the surface composition of the samples fluctuated in Cu:(In, Ga):Se ratio from 1:1:2 to 1:3:5. Conduction band minimum CBM and valence band maximum VBM of the surface region with the 1:1:2 ratio are +0.8 and -0.4 eV with respect to the Fermi level. These numbers agree with those of the chalcopyrite phase with the corresponding Ga concentration. The 1:3:5 region shows a CBM of +0.8 eV and a VBM of -0.9 eV. These are characteristic values of the ordered vacancy compound. The depth profiles of composition of the CIGS layer reveals that the thickness of the 1:3;5-OVC region is no more than 15 nm. Although the lowered VBM of the OVC leads the reduction of the recombination through an expansion of the electron-hole energy separation at the buffer/absorber interface, at the present, this imperfectly cover the surface of CIGS, and thinner than the depletion layer. Morphology and potential distribution of the CIGS surface reveal that small grain size and the variations of built-in potential at grain boundaries. The obtained results indicate that the lateral and depth profiles of the CIGS grown on the polymer substrate are different from those on the glass. Considering that they are dominated by the interdiffusion between the second- and third steps-regions of the CIGS, the present results suggest that there is yet room for improvement in the profiles of the electronic structure by modification of the third stage conditions.
(2) Integration of sputtering apparatus of (Zn, Mg)O buffer with PES/IPES
A multi-target sputtering system has been integrated with the analysis system. The controllability of Composition and optical properties of the (Zn, Mg)O buffers is confirmed. The integration enables to determine the band alignment at the interface between CIGS and the non-Cd buffers without radiation damage, as well as to optimize the composition of the buffer.