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Epitaxial Cu(In,Ga)Se 2 Thin Films on Mo Back Contact for Solar Cells
Author(s) -
Ando Yuta,
Khatri Ishwor,
Matsumori Hironori,
Sugiyama Mutsumi,
Nakada Tokio
Publication year - 2019
Publication title -
physica status solidi (a)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.532
H-Index - 104
eISSN - 1862-6319
pISSN - 1862-6300
DOI - 10.1002/pssa.201900164
Subject(s) - copper indium gallium selenide solar cells , materials science , epitaxy , thin film , crystallite , grain boundary , solar cell , sapphire , sputtering , open circuit voltage , optoelectronics , analytical chemistry (journal) , layer (electronics) , nanotechnology , chemistry , optics , microstructure , metallurgy , voltage , laser , physics , quantum mechanics , chromatography
Single crystal Mo thin films are successfully grown on single‐crystal sapphire {0001} substrates using a newly developed two‐step sputtering method. Cu(In 1‐x ,Ga x )Se 2 (CIGS) thin films are then epitaxially grown on the Mo thin films by three‐stage co‐evaporation. Following that, a CdS buffer layer is deposited on the epitaxial (epi)‐CIGS thin films by a chemical bath deposition (CBD) method, leading to the overall epitaxial relations such as CdS{111}//CIGS{112}//MoSe 2 {0001}//Mo{110}//sapphire {0001}. The Cd‐diffusion into the CIGS occurs to approximately 30 nm from the CIGS/CdS interface boundary together with depleted Cu at the CIGS surface region. This suggests that Cd diffuses through Cu vacancies in the intra‐grain rather than at the grain boundaries. Two distinct solar cells are fabricated using epi‐ and polycrystalline (poly)‐CIGS thin films deposited on sapphire substrates in the same deposition run. The open‐circuit‐voltage ( V OC ) of epi‐CIGS solar cell is found to be higher than poly‐CIGS solar cell. The net carrier concentration ( N CV ) derived from the capacitance‐voltage ( C ‐ V ) measurements of epi‐CIGS solar cell is 3.5 times higher than poly‐CIGS solar cell, suggesting one of the causes of higher V OC . This large difference in the N CV is discussed based on the results of low‐temperature photoluminescence measurements.