World record set by triple-junction perovskite/Si tandem solar cell

The breakthrough by a team from the National University of Singapore (NUS) required the development of a new cyanate-integrated perovskite solar cell that is stable and energy efficient.

Solar cells can be fabricated in more than two layers and assembled to form multi-junction solar cells to increase efficiency. Each layer is made of different photovoltaic materials and absorbs solar energy within a different range. Current multi-junction solar cell technologies pose many issues, such as energy loss which leads to low voltage and instability of the device during operation.

To overcome these challenges, Assistant Professor Hou Yi led a team of scientists from NUS College of Design and Engineering (CDE) and Solar Energy Research Institute of Singapore (SERIS) to demonstrate the integration of cyanate into a perovskite solar cell to develop a triple-junction perovskite/Si tandem solar cell that surpasses the performance of other similar multi-junction solar cells.

“Remarkably, after 15 years of ongoing research in the field of perovskite-based solar cells, this work constitutes the first experimental evidence for the inclusion of cyanate into perovskites to boost the stability of its structure and improve power conversion efficiency,” Asst Prof Hou said in a statement.

The experimental process that led to this discovery has been published in Nature.

The interactions between the components of the perovskite structure determine the energy range it can reach. Adjusting the proportion of these components or finding a direct substitute can help modify the perovskite’s energy range. However, prior research has yet to produce a perovskite combination with an ultrawide energy range and high efficiency.

The NUS team experimented on cyanate, a novel pseudohalide, as a substitute for bromide – an ion from the halide group that is commonly used in perovskites.

Dr Liu Shunchang, a Research Fellow in Asst Prof Hou’s team, employed analytical methods to confirm the successful integration of cyanate into the perovskite structure and fabricated a cyanate-integrated perovskite solar cell.

According to NUS, further analysis of the new perovskite’s atomic structure provided experimental evidence that incorporating cyanate helped to stabilise its structure and form key interactions within the perovskite, demonstrating how it is a viable substitute for halides in perovskite-based solar cells.

The NUS scientists found that perovskite solar cells incorporated with cyanate can achieve a higher voltage of 1.422V compared to 1.357V for conventional perovskite solar cells, with a significant reduction in energy loss.

The researchers also tested the newly engineered perovskite solar cell by continuously operating it at maximum power for 300 hours under controlled conditions. After the test period, the solar cell remained stable and functioned above 96 per cent capacity.

The team took their discovery further by using it to assemble a triple-junction perovskite/Si tandem solar cell. The researchers stacked a perovskite solar cell and a silicon solar cell to create a dual-junction half-cell, providing a base for the attachment of the cyanate-integrated perovskite solar cell.  

Once assembled, the researchers demonstrated that despite the complexity of the triple-junction perovskite/Si tandem solar cell structure, it remained stable and attained a certified world record efficiency of 27.1 per cent.

“Collectively, these advancements offer ground-breaking insights into mitigating energy loss in perovskite solar cells and set a new course for the further development of perovskite-based triple junction solar technology,” said Asst Prof Hou.

Going forward, the NUS team aims to upscale this technology to larger modules without compromising efficiency and stability.