Thin oxide buffer layers for avoiding leaks in CIGS solar cells; a theoretical analysis

Abstract

The purpose of this research is the performance improvement of the CIGS/CdS/ZnO solar cells, while the CdS buffer layer is too thin. Enhancement of photocurrent by decreasing the thickness of CdS buffer layer is expected from a reduced parasitic absorption at short wavelengths. However, the formation of pinholes due to the too-thin CdS buffer layer and a non-uniform coverage of the CIGS surface degrades the solar cell performance by reducing fill factor (FF) and open-circuit voltage (Voc). This degradation is because the direct contact of ZnO and CIGS could exist in pinholes, and the formation of the cliff-like band alignment at CIGS/ZnO interface increases the recombination rate. In this work, to eliminate this destructive effect in the CIGS solar cells with a thin CdS layer, ZnO window layer has been replaced by a suitable thin oxide layer as an intermediate buffer layer. By the proposed oxides, the band alignment between the CIGS layer and the adjacent layer is optimized, while pinholes occurred. It is found that the proposed buffer-less CIGS solar cell leading to the efficiency improvement from 17.6 % to 18.8%.

Efficiency improvement of Cu(In(1−x)Ga x )Se2 solar cell using copper barium tin sulfide as back surface field layer and bandgap grading technique

“…After reducing the Ga content, the electron affinity of the CIGS absorber at the WSSe buffer side becomes higher than the affinity of the WSSe layer, and the cliff-type band In contrast, spike-like band alignment allows for larger built-in potentials. Therefore, interface recombination is reduced due to inadequate holes to recombine with the interface electrons [25]. Hence, the performance of the device is improved by reducing the Ga content at the buffer side.…”

Numerical Investigation of Cu₂O as Hole Transport Layer for High-Efficiency CIGS Solar Cell

“…For these reasons, extensive research is being done on the alternative buffer layer, such as Zinc sulfides, oxides, and selenides [23][24][25][26] . Like CdS, zinc selenide (ZnSe) is an n-type semiconductor but with a wide band-gap and the most promising material to replace CdS [27][28][29][30] . The band-gap of ZnSe is Eg ∼ 2.9 eV which is greater than the CdS Eg ∼2.4 eV, which means more light is passed to the CIGS absorber layer and a larger number of photo-carriers will be generated increasing efficiency.…”

A qualitative Design and optimization of CIGS-based Solar Cells with Sn2S3 Back Surface Field: A plan for achieving 21.83 % efficiency

“…Furthermore, the ZnSe shows optimum performance with a band gap of 2.9 eV [ 18 ]. Imam et al improve the efficiency 21.15 % of CIGS TFSC replaced by the conventional i-ZnO layer with ZnO 1-x S x [ 19 , 20 ] and using different types of HTL boosting the efficiency above 25 % [ [21] , [22] , [23] ]. Reported experimental efficiencies of CIGS TFSC have been found to be 19.2 % [ 24 ], 19.9 % [ 25 ].…”