Credit: Yang et al.
Solar and photovoltaic (PV) panels are becoming more widespread, contributing to ongoing efforts to decarbonize electricity generation. Solar cells based on perovskites, a class of minerals capable of harnessing parts of the solar spectrum, have recently achieved very promising energy conversion efficiencies and stabilities.
Despite these encouraging results, scaling perovskite solar cells has so far proven to be a challenge. Generally, their effectiveness seems to decrease significantly as their surface area increases.
Researchers from Northwestern University, the Institute for Chemical Sciences and Engineering (EPFL), and other institutes around the world recently introduced a new design strategy that could help improve efficiency and stability perovskite solar modules. The proposed method, described in Natural energyinvolves the addition of thermotropic liquid crystals that protect solar cells from environmental stressors and improve their stability.
“Our recent paper stems from the growing need for efficient and stable perovskite solar modules,” Drs Yi Yang and Mohammad Khaja Nazeeruddin, co-authors of the paper, told Tech Xplore.
“We aimed to address the challenges encountered in previous research efforts, drawing on insights from advances in materials science and photovoltaics. Our primary goal was to develop a manufacturing approach that improves efficiency and stability, pushing the limits of perovskite-based solar technology.”
Previous studies exploring the use of liquid crystals to protect perovskite-based solar cells typically used them as routine passivation and hole transport materials. These studies have neglected the thermotropic properties of these crystals, or in other words their movements in response to heat and temperature changes.
Dr. Yang, Dr. Nazeeruddin and their colleagues set out to develop a new additive that exploits these thermotropic properties. The proposed strategy prevents the evaporative crystallization typical of conventional additives and the consequent accumulation of crystals at interfaces, thus ensuring the uniform passivation of large-area perovskite films.
“Previous additives tend to aggregate in the perovskite film upon co-precipitation during solvent evaporation, thereby preventing the movement of charge carriers,” said Drs Yang and Nazeeruddin. “This led us to hypothesize: Exploring alternative processing methods beyond commonly used evaporative precipitation and crystallization could potentially reduce defects and the presence of insulating inclusions.”
The researchers’ recent study suggests that due to their heat-induced phase transition, thermotropic liquid crystals could avoid the aggregation associated with other previously proposed liquid crystal additives. Essentially, they would remain liquid even as the perovskites solidify, facilitating the movement of charge carriers in solar modules for longer periods of time.
“Efficient diffusion within a mixed liquid-solid system allowed the liquid crystal molecules to distribute evenly throughout the film for consistent defect passivation,” the researchers explained.
In initial tests, the new additives proposed by Dr. Yang, Dr. Nazeeruddin and their collaborators achieved encouraging results, giving good stability, a rapid scanning efficiency of 21.8% and a stabilized efficiency of 21.1%. for 30 cm.2 mini perovskite modules. These results could encourage other research groups developing perovskite solar cells to experiment with additives based on thermotropic liquid crystals.
“We introduced a strategy using thermotropic liquid crystals to avoid evaporative precipitation of conventional additives and thus their accumulation at the interface, which enabled uniform passivation of large surface area perovskite films,” added Dr. Yang and Nazeeruddin.
“Our approach can be extended to the slotted array coating maker to fabricate larger surface area perovskite submodules. The functionality and phase structures can be further optimized to improve the crystal growth, performance and stability of the device.”
More information:
Yi Yang et al, A thermotropic liquid crystal enables efficient and stable perovskite solar modules, Natural energy (2024). DOI: 10.1038/s41560-023-01444-z.
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