Molecular engineering strategy improves efficiency of reverse perovskite solar cells

Solar cells, devices that can directly convert radiation emitted by the sun into electricity, are becoming increasingly popular and helping to reduce greenhouse gas emissions around the world. Although existing silicon-based solar cells achieve good performance, energy engineers have sought alternative designs that are more efficient and affordable.

Perovskites, a type of material with a distinctive crystalline structure, have proven particularly promising for the development of low-cost and energy-efficient solar energy solutions. Recent studies have particularly highlighted the potential of inverted perovskite solar cells, devices in which the extracted charge layers are arranged in the reverse order compared to conventional designs.

Inverted perovskite solar cells are more stable than traditional perovskite-based solar cells and may be easier to manufacture on a large scale. Nevertheless, most inverted cells developed so far have been found to have low energy efficiency due to uncontrolled formation of crystal grains that can generate defects and negatively affect the transport of charge carriers generated by sunlight.

Researchers at Huazhong University of Science and Technology recently devised a new molecular engineering strategy to control the crystallization of perovskite materials in inverted solar cells. This promising approach, outlined in a paper published in Nature Energy, involves mixing special naphthalene-based molecules into perovskites to help them grow more uniformly.

“Foramidinium and cesium metal halide perovskites enable high efficiency in inverted perovskite solar cells, but uncontrolled crystallization limits performance,” Qisen Zhou, Guoyu Huang and colleagues write in the paper. “We control perovskite nucleation and growth through aromatic interactions between naphthalene ammonium salts and naphthalene sulfonates.”

Essentially, the researchers mixed naphthalene-based molecules into perovskite solutions to control the formation and growth of perovskite crystals. They found that the resulting perovskite films were uniform and had few defects, which is highly advantageous for the development of inverted solar cells.

“The ammonium group of the naphthalene ammonium salt occupies the formamidinium site, and the sulfonic acid group of the naphthalene sulfonate coordinates with the lead ion,” the authors explained. “Those naphthalene parts are [PbI6]4− Octahedron. These interactions promote regular out-of-plane crystallization along the (100) plane, enhancing defect passivation and carrier transport. ”

Zhou, Huang and colleagues used the uniform perovskite film they created to fabricate inverted perovskite solar cells. We then tested the performance, efficiency, and stability of these cells under continuous illumination.

“We achieved a power conversion efficiency of 27.02% (certified value: 26.88%) with inverted solar cells,” the researchers wrote. “Even after 2,000 hours of maximum power point tracking under continuous illumination in ambient air, the encapsulated device maintains 98.2% of its initial efficiency. Additionally, we demonstrate a certified steady-state efficiency of 23.18% for an inverted mini-module with an aperture area of ​​11.09 cm2 and a certified efficiency of 29.07% for an all-perovskite tandem solar cell.”

The first results collected by this research team are very promising and highlight the potential of molecular engineering approaches in the development of energy-efficient inverted perovskite solar cells. In the future, their strategy could be further refined to achieve further efficiency gains and used to realize high-quality perovskite films of various compositions.

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