Improving efficiency (optimization) of CIGS thin film solar cell using absorbent layer profile change
CIGS thin film solar cell of solid solution combination of Copper-indium-selenide (CIS) and copper -Gallium – selenide CGS is an I-III-VI2 semiconductor which is one of the options to replace silicon solar cell due to high stability and direct band gap, it also has higher yields and lower price compared to other thin film solar cells. In this article, we will initially evaluate the effect of three major factors of thickness, impurity density and band gap of absorber layer which is the most important layer in solar cells on the output parameters including efficiency using AMPS (Analysis of Microelectronic and Photonic Structures) software. Then, for the first time we will provide two important strategies to improve the efficiency of CIGC thin film solar cell. Layers of this type of solar cell are: 1-TCO made of ZnO (zinc oxide) 2- CdS layer gate (cadmium sulphate) with impurities of n 3-CIGS absorber layer with the impurity of p, 4- 5 glass substrate molybdenum layer made of soda. Reduced thickness of the absorbent layer makes the back connection to be closer to the discharge area. Jsc ,Voc , FF and Quantum efficiency (QE) decrease due to absorption of electrons of electrons to the surface of back connection and their participation in recomposition.
Efficiency increases from 20.3399% to 21.3721% by increasing impurity density of absorbent layer and efficiency increases to 28.9266% and the quantum efficiency (QE) doubles by increasing the band gap of absorber layer which is a result of increasing the amount of gallium in CIGS cell. Then, we will achieve the efficiency of 34.1512% which has improved by 5.2246% compared to previous state by providing a way to reduce recombination at the intersection of absorbent / final connection by adding an extra layer made of absorbent layer with more impurities. In the final step, we improved the efficiency by 3.8581% (38.0093%) for the first time by increasing the band gap of CIGS layer. The solar cell used in this cellular thesis has characteristics such as Jsc = 36.7059&, Voc = 0.6721%, FF = 82.4422% and η = 20.3393%.
Keywords: CIGS thin film solar cell, absorbent layer, improving efficiency, quantum efficiency QE, and recombination