NUS develops triple junction tandem solar cells with record efficiency

05 Mar 2024

Perovskite-silicon design offers potential to achieve above 50% conversion efficiency.

Scientists from the National University of Singapore (NUS) have developed a novel triple-junction perovskite/silicon tandem solar cell that can achieve a “certified world-record” power conversion efficiency of 27.1 per cent across a solar energy absorption area of 1 sq cm.

They say that this represents the best-performing triple-junction perovskite/Si tandem solar cell thus far. To achieve this, the team engineered 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. However, 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, for the first time, the successful integration of cyanate into a perovskite solar cell to develop the triple-junction perovskite/Si tandem solar cell.

Asst Prof Hou is a Presidential Young Professor at the Department of Chemical and Biomolecular Engineering under CDE as well as a Group Leader at SERIS, a university-level research institute in NUS.

“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,” said Asst Prof Hou.

The experimental process that led to this ground-breaking discovery is described in Nature (4 March 2024 issue).

Energy-efficient

The interactions between the components of the perovskite structure determine the energy range that 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 recipe with an ultrawide energy range and high efficiency.

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

Further analysis of the new perovskite’s atomic structure provided 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 team then took their discovery to the next level by using it to assemble a triple-junction perovskite/Si tandem solar cell. They stacked a perovskite solar cell and a silicon solar cell to create a dual-junction half-cell, providing an ideal 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 from an accredited independent photovoltaic calibration laboratory.

“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. Future research will focus on innovations at the interfaces and composition of perovskite - these are key areas identified by the team to further advance this technology.