A team of researchers at the National Centre for Photovoltaic Research and Education (NCPRE) at the Indian Institute of Technology Bombay (IITB) has fabricated a semi-transparent perovskite solar cell (PSC) that, by combining it with a silicon-based solar cell, has demonstrated an efficiency of more than 26% for such a cell.
The team at IIT Bombay has addressed the stability issue by combining their PSC with a silicon solar cell in a tandem configuration. Combining the two different types of solar cells allows the device to convert more of the light falling on it into electricity. Apart from the higher efficiency, the tandem architecture also provides greater stability to the device, while driving its overall lifetime costs low.
“Perovskite solar cells are known for their high-power conversion efficiency and lower production cost, however they are lagging in terms of their stability. However, in our work we have fabricated a stable 4T (four terminal) Si/perovskite tandem solar cells which provides outstanding stability in the dark as well as continuous heating conditions”, explained Prof. Dinesh Kabra, a professor at IITB and an author of the new study. A 4T tandem device allows for precise measurements of the solar cell’s performance, while also improving the device’s efficiency and lifetime.
For their study, the team first fabricated a PSC from a thin film of perovskite, which is transparent to near InfraRed light (low-frequency light). The transparency makes them very useful in several devices, including in building integrated photovoltaic (BIPV), vehicle integrated photovoltaic (VIPV) etc. The PSC was then measured for its power conversion efficiency (PCE). The solar cell recorded efficiencies of 17.1% for a small area (0.175cm2) PSC and 16% for a large area (0.805cm2) PSC.
To address the stability issue, the researchers turned to tandem device architecture. They layered the PSC on top of a commercially available silicon solar cell, called Passivated Emitter and Rear Contact (PERC) silicon solar cell. The new tandem structure was far more resilient and stable under different environmental conditions, with a higher demonstrated efficiency. Although the PSC could still degenerate faster than the silicon cell, the fabrication allows for the top PSC layer to be easily replaced. “In our case i.e. in 4T tandem configuration when the top low-cost perovskite solar cells fail, there is a possibility to replace the top cells with a new one because our tandem device is only optically coupled so, it can enhance the lifetime of the overall devices” says Prof. Kabra.
The researchers also demonstrated a 26% power conversion efficiency for the tandem device, which is considered quite high for such a device. “Since there is huge interest in Si/perovskite tandem solar cells, lots of high-efficiency results are coming from the industry, but do not reveal the device architecture and it’s not too useful for academic research progress. Our report not only shows the complete device architecture but also explains the fabrication process, as a typical practice of academic research” commented Prof. Kabra about the academic importance of their work.
In addition, the device lowers the levelized cost of energy (LCOE) for tandem solar cells.
