Abstract
The illuminated current-voltage characteristics of Cu(In,Ga)(S,Se)2 (CIGSSe) thin film solar cells fabricated using two different buffer layer processes: chemical bath deposition (CBD) and atomic layer deposition (ALD) were investigated. The CIGSSe solar cell with the ALD buffer showed comparable conversion efficiency to the CIGSSe solar cell with CBD buffer but lower shunt resistance even though it showed lower point shunt defect density as measured in electroluminescence. The shunt paths were investigated in detail by capturing the high-resolution dark lock-in thermography images, resolving the shunt resistance contributions of the scribing patterns (P1, P3), and depth profiling of the constituent elements. It was found that the concentration of Na from the soda-lime glass substrate played a key role in controlling the shunt paths. In the ALD process, Na segregated at the surface of CIGSSe and contributed to the increase in the shunt current through P1 and P3, resulting in a reduction in the fill factor of the CIGSSe solar cells.
Highlights
Can diffuse into CIGSSe absorber layer on P1 more than that on Mo electrode layer
In order to explain the difference in fill factor loss mechanism of the CIGSSe solar cells via two different buffer layer processes, the shunt paths were investigated in detail by capturing the high-resolution dark lock-in thermography (DLIT) images, resolving the shunt resistance contributions of the scribing patterns (P1, P3), and depth profiling of the constituent elements
From the top view images of the buffer layers, it can be observed that both of the chemical bath deposition (CBD) and atomic layer deposition (ALD) buffer layer showed a good coverage throughout the CIGSSe absorber layer
Summary
Can diffuse into CIGSSe absorber layer on P1 more than that on Mo electrode layer. The Na concentration difference in CIGSSe absorber layer can affect level of the shunt resistance because it causes change in electrical properties of absorber layer including the carrier concentration. The third scribing pattern (P3) is a region where the TCO/Buffer/CIGSSe layers are removed by a needle. The mechanical scribing using a needle can cause formation of many defects in the buffer layer which prevents shunting between the TCO and the CIGSSe absorber layer. In order to explain the difference in fill factor loss mechanism of the CIGSSe solar cells via two different buffer layer processes, the shunt paths were investigated in detail by capturing the high-resolution dark lock-in thermography (DLIT) images, resolving the shunt resistance contributions of the scribing patterns (P1, P3), and depth profiling of the constituent elements
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