Premium
Effect of Cu‐deficient layer formation in Cu(In,Ga)Se 2 solar‐cell performance
Author(s) -
Nishimura Takahito,
Toki Soma,
Sugiura Hiroki,
Nakada Kazuyoshi,
Yamada Akira
Publication year - 2018
Publication title -
progress in photovoltaics: research and applications
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.286
H-Index - 131
eISSN - 1099-159X
pISSN - 1062-7995
DOI - 10.1002/pip.2972
Subject(s) - copper indium gallium selenide solar cells , solar cell , open circuit voltage , analytical chemistry (journal) , transmission electron microscopy , materials science , scanning electron microscope , grain boundary , layer (electronics) , band gap , chemistry , optoelectronics , crystallography , microstructure , nanotechnology , voltage , electrical engineering , composite material , chromatography , engineering
Cu‐deficient layer (CDL) on Cu(In,Ga)Se 2 (CIGS) promotes Cd diffusion from CdS buffer layer and forms a valence band offset (Δ E V ) between CDL and CIGS. We quantitively demonstrate the effects of CDL formation on the performance of CIGS solar cells through experiments and theoretical simulation. To investigate the effects of Cd diffusion and Δ E V by CDL, theoretical analysis was carried out for a CIGS solar cell with a surface layer which simulated the CDL at CdS/CIGS interface. It was revealed that when electron concentration in n‐type surface layer is higher than the absolute carrier concentration in CIGS absorber ( N D > | N A, CIGS |), open‐circuit voltage and fill factor are improved. Additionally, Δ E V ≥ 0.15 eV leads to the highest open‐circuit voltage by suppression of interfacial recombination. Transmission electron microscope energy dispersive X‐ray spectrometry and scanning spreading resistance microscopy were employed for the same cross section of a CIGS solar cell fabricated by three‐stage process. Despite CDL with Cu/(Ga + In) of 0.31 formed on the surface had high Cd contents of 3.4 at%, its carrier concentration of 4.8 × 10 10 cm −3 was lower than that of 10 14 –10 16 cm −3 in grain interior owing to insufficient activation of Cd atoms. These results indicate the effectiveness of Δ E V formation by introducing CDL with low Cu/(Ga + In) of 0.31 to boost CIGS solar cell performance and difficulty in realizing N D > |N A, CIGS | by surface Cd doping.