Impact of Buffer Layer Process and Na on Shunt Paths of Monolithic Series-connected CIGSSe Thin Film Solar Cells

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.

Anisotropic Charge Transport in Cu(In,Ga)Se2 by Heavy Alkali Postdeposition Treatment for Reducing Cell‐to‐Module Efficiency Loss in Monolithically Integrated Photovoltaic Modules

“…In fact, the same shunt resistance value was reported to initiate FF drop of a CIGS cell. [ 11 ] Given the parallel nature, the total shunt resistance becomes low if any of the three shunt resistances above is dominantly low. Therefore, we would like to quantify each shunt resistance value directly from the fabricated modules so as to determine which shunt path dominates the low FF in the module with NaF PDT.…”

“…[ 10 ] Na accumulation on the absorber surface was reported as the origin of the high P1 shunt current which could be lessened by a postalkali rinsing step or a different buffer layer process. [ 11 ] Short‐range heat effect due to laser scribing observed by photoluminescence (PL) mapping suggested a change of the CIGS property into a metallic character near the P1‐scribed Mo edge, but such an edge effect would not completely explain the P1 shunt current behavior in the long range. [ 12 ]…”

The Diagnosis of Shunt Defects in CIGS Modules Using Lock-In Thermography: An Empirical Comparative Study

“…We present an analysis of a CIGS mini-module by employing a system capable of both biased thermography and LIT. Through a comparison analysis, we demonstrate the efficacy of these two techniques and identify scenarios in which biased thermography performed adequately [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19]. We also provide an in-depth discussion of the advantages and limitations of each thermography method when diagnosing shunt defects in CIGS modules.…”

“…However, there remains a challenge in many laboratories where commercially available LIT systems are used without a comprehensive understanding of the respective strengths and drawbacks of each method. This study aimed to address this knowledge gap by conducting a comparative analysis of biased thermography and LIT, focusing on investigating shunt defects in CIGS modules [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19].…”