An international team of scientists at King Abdullah University of Science and Technology (KAUST), Fraunhofer Institute for Solar Energy Systems (ISE), and University of Freiburg has developed a new method that significantly boosts the performance and stability of solar cells. The enhancement comes from treating the perovskite surface of perovskite silicon tandem solar cells with a single molecule. For countries embracing solar energy, the finding has the potential to save billions of dollars.  

The innovation enabled tested solar cells to achieve a conversion efficiency of 33.1% and a record open-circuit voltage of 2.01 volts, two critical metrics for solar cells. Moreover, the treated devices maintained improved performance while operating along the Saudi coast at over 40 C and for over 1500 hours. Extreme heat has been proven to compromise solar cells by overheating the electronics.  

The conversion efficiency is a reminder of why industry is heavily investing in perovskite silicon tandem solar cells compared with the more standard silicon solar cells, whose physical efficiency limits do not exceed 30%. By stacking a perovskite cell on top of a silicon cell, perovskite silicon tandem solar cells allow for better use of the solar spectrum, capturing more energy from sunlight.  

For large-scale production of these tandem solar cells, using a standard silicon solar cell for the bottom cell would be advantageous, as their manufacturing processes are already well established. These solar cells are textured to increase their surface area, enhancing efficiency, but this texturization also complicates the deposition of the perovskite layer. Achieving high-quality surface passivation of the perovskite top cell on the pyramid-like surface had not yet been accomplished. 

"So far, effective passivation has not been fully harnessed on textured perovskite silicon tandem solar cells, with prior success largely confined to flat-front architectures. But we have now managed excellent passivation by depositing 1,3-diaminopropane dihydroiodide [PDAI] on the uneven perovskite surface," said Dr. Oussama Er-Raji, one of the lead authors of the paper and a scientist at Fraunhofer ISE, of the molecule that enabled the superior solar cell performance. 

PDAI created a beneficial electrical effect across the entire perovskite layer. Unlike in conventional silicon solar cells, where surface treatment affects only the surface, treating the perovskite layer with PDAI improved the bulk properties of the perovskite layer itself, boosting conductivity and overall performance. 

"This realization provides a solid foundation for all future research in this area,” said KAUST Prof. Stefaan De Wolf, another lead author. “It enhances our understanding of the processes occurring in the top cell while converting light into electricity, enabling scientists to leverage this knowledge to develop better tandem solar cells." 

"The experiments done at KAUST were crucial, as the combination of interdisciplinary experts and world class facilities significantly accelerated the research," added Er-Raji. 

As Saudi Arabia invests heavily in solar energy, this achievement underscores the Kingdom’s growing role as a hub for renewable energy research and innovation. It also demonstrates the importance of KAUST in shaping this transition, both through excellent science and international partnerships.