Enhancement of the photo conversion efficiencies in Cu(In,Ga)(Se,S)2 solar cells fabricated by two-step sulfurization process

Cu(In,Ga)(Se,S)2 (CIGSS) absorber layers were fabricated by using a modified two-stage sputter and a sequential selenization/sulfurization method, and the sulfurization process is changed from one-step to two-step. The two-step sulfurization was controlled with two different H2S gas concentrations d...

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Bibliographic Details
Published in:Applied physics letters 2015-11, Vol.107 (19)
Main Authors: Yang, JungYup, Nam, Junggyu, Kim, Dongseop, Kim, GeeYeong, Jo, William, Kang, Yoonmook, Lee, Dongho
Format: Article
Language:English
Subjects:
Absorbers
Applied physics
Circuits
Grain boundaries
Hydrogen sulfide
Mass production
Microscopy
Open circuit voltage
P-n junctions
Passivity
Photovoltaic cells
Scanning electron microscopy
Secondary ion mass spectrometry
Selenium
Short circuit currents
Solar cells
Sulfurization
X-ray diffraction
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Summary:Cu(In,Ga)(Se,S)2 (CIGSS) absorber layers were fabricated by using a modified two-stage sputter and a sequential selenization/sulfurization method, and the sulfurization process is changed from one-step to two-step. The two-step sulfurization was controlled with two different H2S gas concentrations during the sulfurization treatment. This two-step process yielded remarkable improvements in the efficiency (+0.7%), open circuit voltage (+14 mV), short circuit current (+0.23 mA/cm2), and fill factor (+0.21%) of a CIGSS device with 30 × 30 cm2 in size, owing to the good passivation at the grain boundary surface, uniform material composition among the grain boundaries, and modified depth profile of Ga and S. The deterioration of the P/N junction quality was prevented by the optimized S content in the CIGSS absorber layer. The effects of the passivation quality at the grain boundary surface, the material uniformity, the compositional depth profiles, the microstructure, and the electrical characteristics were examined by Kelvin probe force microscopy, X-ray diffraction, secondary ion mass spectrometry, scanning electron microscopy, and current-voltage curves, respectively. The two-step sulfurization process is experimentally found to be useful for obtaining good surface conditions and, enhancing the efficiency, for the mass production of large CIGSS modules.
ISSN:0003-6951
1077-3118
DOI:10.1063/1.4935333