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Over 14% Efficiency of Directly Sputtered Cu(In,Ga)Se 2 Absorbers without Postselenization by Post‐Treatment of Alkali Metals
Author(s) -
Hsu ChiaHao,
Ho WeiHao,
Wei ShihYuan,
Lai ChihHuang
Publication year - 2017
Publication title -
advanced energy materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 10.08
H-Index - 220
eISSN - 1614-6840
pISSN - 1614-6832
DOI - 10.1002/aenm.201602571
Subject(s) - copper indium gallium selenide solar cells , materials science , sputtering , passivation , alkali metal , doping , thin film , optoelectronics , layer (electronics) , nanotechnology , chemistry , organic chemistry
Direct sputtering of a single quaternary Cu(In,Ga)Se 2 (CIGS) target without postselenization is a promising approach to fabricating CIGS absorbers. However, the device efficiency of the quaternary‐sputtered CIGS is limited to 10%–11% due to the low and uncontrollable Se supply during the quaternary sputtering process. Here, an enhanced efficiency of 14.1% is reported by directly sputtering from a CIGS target without extra Se supply followed by sequential postdeposition treatments (PDT) of NaF and KF. The effects of different post‐treatments of alkali metals on quaternary‐sputtered CIGS thin films are discussed in detail. A Cu‐depleted surface is not observed in the quaternary‐sputtered CIGS thin films after KF‐PDT, different from the observation in the coevaporated CIGS, in which the Cu‐depleted surface layer induced by KF‐PDT enhances the efficiency. On the other hand, it is found that KF‐PDT reduces Se vacancies more effectively than NaF‐PDT, which could be another electrically benign behavior of KF‐PDT. The effective passivation of Se vacancies after KF‐PDT overcomes the Se‐poor nature of the quaternary sputtering process without postselenization. Therefore, KF‐PDT combined with Na doping, which is known to annihilate In Cu defects, significantly improves minority carrier lifetime and cell performance.