Improving Stability and Efficiency of Bifacial Perovskite Solar Cells Through New Design Strategies

May 15, 2023 feature

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by Ingrid Fadelli , Tech Xplore

Solar cells made from perovskites, a calcium titanium oxide mineral with similar structures, are among the most promising energy solutions. Over the years, engineers and material scientists have been exploring the potential of solar mini-modules, which are small cells used to create solar panels, made from bifacial perovskite structures.

These flat structures have perovskite materials on both their front and back sides, with the first harvesting direct sunlight and the latter harvesting reflected light. While solar mini-modules based on perovskite bifacial structures could achieve greater power conversion efficiencies (PCEs) than conventional perovskite solar cells, designing them has so far been difficult.

Recently, researchers at the University of North Carolina at Chapel Hill introduced new design strategies to improve the efficiency and stability of bifacial perovskite solar cells. Using these techniques, they developed new solar mini-modules that achieved remarkable efficiencies.

'Perovskites solar cells are booming with quickly rising efficiencies and commercialization of them are moving fast globally, but there are still many remaining challenges to overcome, including low stability and the derate of efficiency when transferring from low-scale small cells to large-area modules,' said Jinsong Huang, one of the researchers who carried out the study. 'One uncertainty is whether the cost-saving of using low-cost perovskites and deposition processes is sufficient to compete with fossil fuel-based energy.'

Bifacial solar cells can improve the energy yield of solar technologies. So far, however, researchers developed only a few bifacial perovskite cells and modules, and existing ones exhibited far lower efficiencies than their mono-facial counterparts.

'The goal of our recent work was to demonstrate perovskite bifacial mini-modules with high energy yield and long operational lifetimes,' Huang said. 'The main strategies we propose for the design optimization of bifacial perovskite modules include a newly designed module structure and rear electrode, adding hydrophobic additives for improved moisture stability, and enhancing long-wavelength light absorption with embedded dielectric nanoparticles.'

Huang and his colleagues firstly designed a bifacial structure in which individual sub-cells are connected by indium tin oxide (ITO), and with silver grids that are separated by an optimal space on the rear ITO electrode to reduce resistance loss. This design is straightforward and scalable, which means that it could enable the large-scale fabrication and commercialization of perovskite bifacial mini-modules.

'We also found that adding tris(pentafluorophenyl)borane (TPFB) as an additive in the hole transport layer obviously alleviated the damage of moisture to the perovskite film during the process of SnO2 deposition,' Huang explained.

'Besides, the addition of TPFB decreased the resistivity of the hole transport layer and enhanced the energy alignment. Finally, we introduced nanoparticles (NPs) into the perovskite to scatter the incident sunlight, thereby increasing the optical path to overcome their absorption loss particularly in the long-wavelength range in bifacial modules.'

Using their proposed design, the researchers developed small-area bifacial perovskite solar cells that achieved a power generation density of 26.4 mW cm-2 and bifacial mini-modules that achieved a power generation density of 23 mW cm-2, when exposed to direct sunlight on one side and with an albedo illumination of 0.2 on the other. These results are significantly better than the power generation densities exhibited by previously developed perovskite single-junction solar cells and mini-modules.

Remarkably, the prototype minimodule developed by the team was also found to achieve a remarkably operational stability, only losing 3% of its initial efficiency after working for more than 6,000 hours. Combined, the design strategies introduced by this team of researchers could thus pave the way towards the large-scale fabrication of highly efficient and stable solar energy solutions based on bifacial perovskite structures.

'While some companies may already be working on commercializing perovskite bifacial solar cells, this work affirms the promising potential of these bifacial structures,' Huang added. 'We would now like to identify new strategies to continually improve the energy yield and stability of bifacial perovskite solar modules.'

More information: Hangyu Gu et al, Design optimization of bifacial perovskite minimodules for improved efficiency and stability, Nature Energy (2023). DOI: 10.1038/s41560-023-01254-3

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