This paper indicated a theoretical investigation of a CIGS based solar cells. An optimum value of the thickness of this structure has been calculated and it is shown that by optimizing the thickness of the cell efficiency has been increased and cost of production can be reduced. Numerical optimizations have been done by adjusting parameters such as the combination of band gap and mismatch as well as the specific structure of the cell. It is shown that by optimization of the considered structure, open circuit voltage increases and an improvement of conversion efficiency has been observed in comparison to the conventional CIGS system.
Thin film solar cells are large area diodes tailored to enable and maximize the absorption of light within a short distance from the space charge region of solar cells and offer a number of interesting advantages compared to the bulk silicon devices, which are fairly complicated and expensive to produce [1], [2] and [3]. Chalcopyrite Cu(In,Ga)Se (CIGS) is a very promising material for thin film photovoltaics and also, chalcopyrite based solar modules uniquely combine advantages of thin film technology with the efficiency and stability of conventional crystalline silicon cells [3], [4], [5], [6], [7] and [8].
Highest efficiencies for CIGS solar cells are commonly obtained by the vacuum evaporation method using sophisticated multistage growth processes that induce favorable growth of large and smooth grains in CIGS [5]. Cu(InGa)Se2 (CIGS)-based thin film solar cells have up to now yielded efficiencies of up to 19.9% [3] and [9]. CIGS absorbers today have a typical thickness of about 1.5–2 μm. However, on the way towards mass production, it will be necessary to reduce the thickness even further [6].
The main reasons for this are material costs, the fact that indium and gallium resources are limited, and the need to cut the process duration in order to achieve a higher output of the production [8]. So far, absorbers down to a thickness of about 0.5 μm have already been achieved with no or only little reduction of the open-circuit voltage and the fill factor [10]. But, the short-circuit current density is decreased significantly in those devices, as the absorber thickness is no longer much larger than the absorption. CIGS devices are typically fabricated in a substrate configuration by sequentially depositing metal and semiconductor layers on a suitable base substrate (Fig. 1). In order to attain cost efficient fabrication of solar cells, materials capable of low-cost production are required [8] and [11]. Furthermore, to optimize the full efficiency potential from low-quality wafers, the effects of the higher impurity contents on the cell performance should be studied. In order to increase the efficiency of the cell toward the ideal one, it is necessary to reduce the sum to losses in the cell [11] and [12].
In this paper, in order to investigate the effects of cell composed layers’ thickness on the performance of the cell, a typical CIGS solar cell structure which it is composed of six layers, namely a transparent conductive oxide (TCO) contact which composed of ZnO:Al, an n-doped ZnO layer, an n-doped CdS buffer layer, an p-doped Cu(In1−xGax)Se2 layer, and a molybden metal contacts, and a glass substrate, as shown in Fig. 1, were simulated by SCAPS simulation software [12] and [13]. This paper indicated a simulation study to optimize the CGIS based thin film solar cells. An optimum value of the thickness of this structure has been calculated and it is shown that by optimizing the thickness of the cell efficiency has been increases and cost of production can be reduces.
This paper indicated a theoretical investigation of a CIGS based solar cells. Numerical optimizations have been done by adjusting parameters such as the combination of band gap, mismatch, etc., as well as the specific structure of the cell. From the simulation results it was fund that by optimization of the considered structure, optimized value of CIGS and TCO thickness is 0.3 μm and 20 nm and an improvement of conversion efficiency has been observed in comparison to the conventional CIGS which cell efficiency increases from 16.75% to 20.34%, respectively.
