Linking two solar technologies to improve both efficiency and stability

Win-win for efficiency and stability.

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A number of high-performance solar systems have been quickly made possible by metal halide perovskites. However, their commercialization could be improved by catastrophic failure under reverse voltage bias.

In a new study, scientists from Princeton University and the King Abdullah University of Science and Technology (KAUST) connected the well-established silicon solar cell with the up-and-coming perovskite in a tandem solar cell to boost overall efficiency and strengthen stability. They found that the connection achieves higher efficiency than either cell can independently while saving the vulnerable perovskite solar cell from voltage-induced breakdown.

Barry Rand, research leader and professor of electrical and computer engineering at the Andlinger Center for Energy and the Environment, said, “Tandem solar cells have already demonstrated power conversion efficiencies greater than either silicon or perovskite solar cells alone. While best-in-class efficiencies for silicon and perovskite solar cells have hovered around 27% and 26%, respectively, tandem devices have demonstrated efficiencies over 33% in less than a decade of research.”

“We thought that in addition to their higher efficiencies, tandem solar cells could also solve some of the stability challenges facing perovskites by linking them with silicon cells, which are much more stable.”

The scientists constructed three strings of solar cells to test their theories: one with only silicon solar cells, one with only perovskites, and one with tandem solar cells made of the two technologies linked in series. Scientists then shaded one of the cells in the string to simulate partial shading conditions that a solar array may experience at least once throughout its decades-long lifespan.

Perovskites are typically doomed by partial shading because the still-illuminated cells push charge to flow through the now-inactive and shaded cell, rapidly destroying it and the module. Contrarily, silicon solar cells are far more resistant to voltage fluxes and may function generally during periods of partial shadowing.

Unlike the perovskite-only solar module, the silicon solar module was slightly affected, which rapidly degraded following partial shadowing. Intriguingly, the tandem solar module proved equally durable as the silicon-only module, suggesting that by combining the two solar technologies, the silicon cell could conceal the perovskite’s weakness.

Co-author Stefaan De Wolf, professor of material science and engineering at KAUST, said, “When you combine two different materials to form a final product, usually it’s the weakest link that determines the overall strength of the chain. But in this case, the stronger component protected the weaker one.

“Their findings demonstrate that partial shading — a major obstacle to perovskite-only modules — may be a negligible concern for series-connected tandem solar devices.”

“The findings bode well for the commercialization prospects of perovskites because they imply that perovskites may have the most potential when deployed in complement with silicon solar cells, for which a mature manufacturing ecosystem already exists. Instead of having to build a competing manufacturing process, perovskites could be added onto the commercially proven production process for silicon solar cells.”

They said tandem devices could enable solar research to develop after silicon solar cells hit their upper power conversion efficiency limits. However, several problems, in addition to partial shading, still need to be resolved before tandem solar cells achieve the lifespan anticipated by commercial solar technologies, such as their poor resilience to heat.

Rand said, “If some other stability challenges can be solved, tandem solar cells could take an already successful commercial technology and make it even better. Our results make a strong case that tandem devices should be an all-hands-on-deck area for future solar research.”

Journal Reference:

  1. Zhaojian Xu, Helen Bristow, Maxime Babics, et al. Reverse-bias resilience of monolithic perovskite/silicon tandem solar cells. Joule. DOI: 10.1016/j.joule.2023.07.017
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