Solar energy is among the most significant green and renewable energy sources that have been considerably exploited. Importantly, it is already playing a substantial role in realizing sustainable energy solutions. Solar energy has numerous benefits, including being environmentally friendly, abundant in nature, cost-effective and increasing energy independence. Owing to its importance, a significant amount of research efforts has been devoted to improving the photovoltaic performance of various solar cells.
While crystalline silicon (c-Si) solar cells have been widely used in the production of photovoltaic cells in the last decades, the recent development of bifacial c-Si photovoltaic modules seems to be a game changer. Unlike monofacial c-Si solar cells, bifacial c-Si photovoltaic cells can achieve an increase in energy output exceeding 25% by collecting the front and ground-reflected light simultaneously, which dominate the current industrial solar cells. To this end, the market share of bifacial photovoltaics is projected to tremendously increase to up to 70% in the next decade. From this application trend, a huge potential market for bifacial perovskite/c-Si tandem solar cells can be foreseen due to the higher energy yield with the same light area compared to the bifacial c-Si counterparts. Perovskite solar cell is widely proposed to be a suitable tandem partner with c-Si solar cell due to its significant advantages of large absorption coefficient, tunable bandgap, low-cost preparation.
Recent findings have revealed that bifacial perovskite/c-Si solar cells have greater energy harvesting superiority than monofacial devices. However, there is a lack of sufficient experimental investigation on this cutting-edge and complex technology, because the series in bifacial perovskite/c-Si tandem solar cell prevents the detailed analysis on each sub-cell and the influence of the sub-cells on the tandem cell. In particular, experimental studies have found the efficiency of bifacial perovskite/c-Si tandem solar cells to be much lower than the theoretical value, which is mainly attributed to current matching loss (CML). This has made it difficult to hinder the calculation of the various photovoltaic parameters of solar cells.
To overcome the above limitations, Dr. Daxue Du, Mr. Chao Gao, Professor Wenzhong Shen from Shanghai Jiao Tong University together with Professor Haiyan Wang from Yanshan University investigated the photovoltaic performance of the bifacial sub-cells of bifacial perovskite/c-Si tandem solar cells. In their approach, they graphically analyzed the characteristics of current in the sub-cells current under bifacial illumination and proposed an approach for determining the photovoltaic performance of the bifacial sub-cells. Additionally, an effective and feasible approach for calculating the CML of the bifacial perovskite/c-Si tandem cells was proposed. Their work is currently published in the research journal, Journal of Power Sources.
The authors obtained the photovoltaic performance of bifacial perovskite/c-Si tandem solar cells under various perovskite bandgaps and albedos. A greater rear illumination intensity than that of matched albedo resulted in a gradual improvement in the photovoltaic performance and a prompt rise in the CML, which further resulted in energy wastage. Also, a maximum matched albedo for perovskite bandgaps of 1.55 to 1.75 eV was 18.1%, which could be adequately satisfied by albedo of common ground materials.
Furthermore, it was noted that establishing the numerical relationship between the bifacial tandem cells and the bifacial sub-cells based on the energy balance principle is of great importance in determining the CML. The daily and annual energy loss and energy yield of bifacial tandem solar cell were forecast in different latitude regions. The simulation results agreed well with the experimental observations, indicating the feasibility and reliability of the proposed methods. This method was versatile and could be extended to monofacial tandem cells.
In summary, the study offered a series of solutions to address the inherent photovoltaic performance issues of monofacial and bifacial sub-cells as well as perovskite/c-Si tandem solar cells. Unlike existing methods, the proposed approach successfully determined the numerical relationship between the bifacial tandem cells and bifacial sub-cells from the principle of energy balance. In a statement to Advances in Engineering, Professor Wenzhong Shen explained that their findings would provide a framework for improving energy yield and reducing losses to enhance the efficient application of perovskite/c-Si tandem solar cells.
Du, D., Gao, C., Wang, H., & Shen, W. (2022). Photovoltaic performance of bifacial perovskite/C-Si tandem solar cells. Journal of Power Sources, 540, 231622.