The heterojunction solar cell consists of CdS, BaSi2 and Cu2O as buffer, absorber and BSF layers respectively under AM1.5 conditions were simulated. The width of BSF and absorber layers varies to examine the cell performance whereas the other factor remain same. The value of Jsc have been attained up to 35.5 mAcm-2 with to 24.4 % efficiency based on our recommended structure.
3.1. Effect of width of absorber (BaSi2) layer
The impact of change in the width of BaSi2 layer on the device performance is demonstrated in table 2 and Fig. 2. The width of BSF were maintained as 0.2 µm, however, for both CdS and ZnO layers value of thickness is 0.1 µm. Excessive number of carriers are generated due to incident photons absorption in the BaSi2 layer that is the extremely substantial part of solar cell. In this work we examine the effect of BaSi2 layer width on the suggested heterojunction solar cell limitations with varying thickness of BaSi2 layer up to 5 µm. Major device limitations such as Voc, Jsc and η were depicted and simulated in fig. 2. The outcomes reveals that Jsc and FF rises as the BaSi2 layer width increase. The main cause of this kind of trend is primarily ascribed to enhanced absorption of incident light due to wider absorber layer [25]. The BaSi2 layer has been absorbed significant amount of incident photons with the rise of width of layer which precedes to the increase in photo electrons. The increase in the possibility of SRH (Shockley-Read-Hall) recombination because of growth of BaSi2 layer width leads to the decrease in η and Voc. Though, the width of absorber layer is directly impacting the cost of material which is the major drawback of solar cell with thicker absorber layer [25]. Hence, we are setting up the layer width to augmented value of 5 µm in present work. 5 µm BaSi2 layer width permits to provide the η of about 24.3% and Voc of 0.82 V.
3.2. Effect of thickness of BSF (Cu2O) layer
A large doping concentration plays an important role at rear side of cell, to prevent the carriers’ recombination due to metallic rear contact. As a result, a BSF (back surface field) film is establishes having larger doping concentration than absorber layer. A thin layer of Cu2O is merged to BaSi2 and act as BSF region. The impact of change in Cu2O width on working of device is demonstrated in table 3 and Fig. 3. The BaSi2 and CdS width is 5 and respectively even as Cu2O width changing from to . It can be noticed from the results that as the change in Cu2O layer width do not affect the cell parameters (Voc, Jsc, FF, η) significantly. At the Cu2O/BaSi2 interface, an electric field is created which behave as space charge region (potential barrier) for drift of minority carriers to back surface. A 0.2 µm thick BSF layer permits the Jsc of ~ 35.656 A/cm3 as well as the efficiency of about 24.27%.
3.3. Effect of operating temperature
Operating temperature directly affects the stability of solar cell, as it is described in previous research that Voc changes with the change in operating temperature. Fig. 4 demonstrated that the temperature changes between 300 and 600 K on the way to examine the implementation of defected CdS/BaSi2/Cu2O thin film solar cell. As displayed in fig 4 (a) the Voc reduces due to rise in temperature. With the rise of operating temperature, bandgap of bandgap decreases which also leads to growth in leakage current. An insubstantial variation can be noticed in Jsc, though, Voc reduces constantly from 0.8 to 0.2V. The η and FF are also demonstrating the analogous trand of decline from 85 to 45% and 24.5% to 2.3% respectively.
3.4. Effect of variation in the concentration of defect density
Solar cell performance parameters are directly affected by a significant factor known as defect density. Absorber layer plays a crucial role in generating the photo-electric current. Therefore, the carrier recombination increases due to increase in defect density which leads to the decrease in device efficiency. We change the defect density from 1012 cm-3 to 1019 cm-3 to study the impact of defect density on the performance of device. It is observed that the defect density influences the output of device in a substantial manner as demonstrated in fig. 5. One can be noticed from fig. 5 that the Jsc starts decreasing when defect density increases above 1016 cm-3. However, the efficiency decreases continuously with increase in defect density from 1012 cm-3 to 1019 cm-3. The results are in good agreement with the previous studies [26]. The carrier recombination increases due increase in defect density which in order decrease the diffusion length and carrier lifetime, hence, the overall performance of device decreases.