New solar cells break efficiency record

Researchers successfully integrated a new anion, cyanate, into a perovskite structure, which was a key breakthrough in fabricating new triple-junction perovskite/Si tandem solar cells. (Credit: NUS)

Researchers have invented new solar cells with world-record efficiency.

The triple-junction perovskite/Si tandem solar cell can achieve a certified world-record power conversion efficiency of 27.1% across a solar energy absorption area of 1 sq cm (0.155 sq in), representing 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 at the National University of Singapore (NUS) led a team of scientists from the 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 a cutting-edge 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,” says Hou, a professor at the chemical and biomolecular engineering department under CDE as well as a Group Leader at SERIS.

The experimental process that led to this ground-breaking discovery is detailed in Nature.

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 this recently published work, the researchers experimented on cyanate, a novel pseudohalide, as a substitute for bromide—an ion from the halide group that is commonly used in perovskites. Liu Shunchang, research fellow in 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—for the first time— experimental evidence that incorporating cyanate helped to stabilize its structure and form key interactions within the perovskite, demonstrating how it is a viable substitute for halides in perovskite-based solar cells.

When assessing performance, the researchers found that perovskite solar cells incorporated with cyanate can achieve a higher voltage of 1.422 volts compared to 1.357 volts 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% capacity.

Encouraged by the impressive performance of the cyanate-integrated perovskite solar cells, the researchers took their ground-breaking discovery to the next level 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 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% 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,” says Asst Prof Hou.

Theoretical efficiency of triple-junction perovskite/Si tandem solar cells exceeds 50%, presenting significant potential for further enhancements, especially in applications where installation space is limited.

Going forward, the 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.

Source: National University of Singapore