Optimization of Three-terminal Perovskite/Silicon Tandem Solar Cell Using Opto-electrical Simulations in TCAD Sentaurus

Abstract

Perovskite/Silicon tandem cells are gradually becoming more promising in the field of photovoltaic technology since they have already surpassed the theoretical power conversion efficiency (PCE) limit of single junction (SJ) silicon cells (~30%), while they can be commercially compatible. Several architectures of Perovskite/silicon devices were proposed. The most known of them are four terminals tandem (4TT) and two terminals tandem (2TT). Which are well researched and have already surpassed the highest efficiency achieved by SJ silicon cells. On the other hand, 3TT is less known architecture which have received less attention in research than 2TT and 4TT but seems to combine the advantages of both and eliminate their disadvantages. Although of the few research done on 3TT, they revealed great potential of achieving high efficiency. Yet it is still practically challenging to design and fabricate stable 3TT devices that bring 30% PCE’s goal to reality. To continue unveiling the potential of 3TT perovskite/Si device, more research needs to be done in areas that haven’t been investigated before. And that was the target of this project.
The 3TT device structure proposed in this work is a perovskite top cell on a c-Si IBC bottom cell. And the focus of the project was to investigate and optimize the design parameters of the perovskite top cell as well as the IBC bottom cell to improve the overall efficiency of the tandem device using 2D modelling. To achieve these Objectives, a 2-D simulation model template was built for the mentioned tandem device with the help of Sentaurus TCAD. Further, the model template has been validated. Subsequently, the validated model was used to conduct a comparison between the proposed 3TT device and an identical 4TT device to examine the compactivity of the model with other tandem configurations. This has shown that the 3TT model has performed as good as the 4TT model. Both models showed capability of achieving efficiency beyond 30%.
Then, the performance of the 3TT model was examined under different thicknesses of Perovskite layer. This revealed that the 3TT device has the highest efficiency when the perovskite layer has a thickness between 0.5 - 1.2 µm where efficiency higher than 30% can be achieved.
The next step was to investigate and redesign the IBC bottom cell to improve the 3TT performance. First, the device performance under different pitch values in the IBC bottom cell was examined. It was found that the lower the pitch is, the higher the performance becomes. It was also found that the pitch value doesn’t influence only the bottom cell but also the top cell. Which makes the performance of 3TT device more sensitive to pitch values than the SJ IBC cell. Second, the rear emitter to base ratio in the IBC bottom cell was investigated. Which showed that the emitter/base ratio has less influence on the 3TT behavior when the pitch value is within or less than the range of the diffusion length of the bulk material. But the influence of the ratio grows up when the pitch is higher. The 3TT device has its peak performance when the ratio is between 2:1 to 4:1.
After that, the tandem model was redesigned to corporate all the outcomes that was found in previous steps. This resulted in several scenarios based on best parameters to design 3TT models with the best outcome. Four scenarios have been suggested where each of them can achieve PCE higher than 31.5 %.
Finally, we have studied the effect of surface recombination on the performance of the 3TT device. Which revealed that most of surface recombination losses are coming from the interfaces between perovskite layer and ETL or HTL layers. Therefore, if these surface recombination losses are suppressed, that will lead to a PCE higher than 33 %.