New approach to advance perovskite solar cell manufacturing

Perovskite solar cells (PSCs) are a promising candidate for next-generation photovoltaic technology due to their high efficiency and low production cost. However, the existing layer-by-layer manufacturing process presents challenges that have hindered the commercialisation of this technology. Researchers from City University of Hong Kong (CityU) and the National Renewable Energy Laboratory (NREL) in the US jointly developed an innovative one-step solution-coating approach that simplifies the manufacturing process and lowers the commercialisation barriers for PSCs.

Dr Zhu Zonglong, a co-leader of the research, said reducing the number of device-processing steps without sacrificing device efficiency will help reduce the process complexity and manufacturing cost, thereby enhancing the manufacturability of PSCs. “We addressed the manufacturing issue with a novel approach to co-process the hole-selective contact and perovskite layer in a single step, resulting in state-of-the-art efficiency of 24.5% and exceptional stability for inverted perovskite solar cells. This helps bring the commercialisation of the technology one step closer,” Zhu said.

Typically, PSCs are fabricated using a layer-by-layer process, which involves sequentially depositing different layers of the solar cell on top of each other. While this approach has been successful in producing high-performance perovskite solar cells, it causes issues that may hinder their commercialisation, such as increased fabrication cost, unsatisfactory uniformity and reproducibility. To improve the manufacturability of PSCs, the researchers developed a new approach for fabricating efficient inverted perovskite solar cells in which the hole-selective contact and perovskite light absorber can spontaneously form in a single solution-coating procedure.

They found that if specific phosphonic or carboxylic acids are added to perovskite precursor solutions, the solution will self-assemble on the indium tin oxide substrate during perovskite film processing. They form a robust self-assembled monolayer as an excellent hole-selective contact while the perovskite crystallises. This single solution-coating procedure solves wettability issues and simplifies device fabrication by creating both the hole-selective contact and the perovskite light absorber simultaneously, instead of the traditional layer-by-layer process.

The new PSC device has a power conversion efficiency of 24.5% and can retain more than 90% of its initial efficiency even after 1200 hours of operating at the maximum power point under continuous illumination. Its efficiency is reportedly comparable to that of similar PSCs in the market. The researchers also showed that the new approach is compatible with various self-assembled monolayer molecular systems, perovskite compositions, solvents and scalable processing methods, such as spin-coating and blade-coating techniques. The PSCs fabricated with the new approach have comparable performance with those produced from other methods.

“By introducing this innovative approach, we hope to contribute to the perovskite research community by proposing a more straightforward method for manufacturing high-performance perovskite solar cells and potentially accelerating the process of bring them to market,” Zhu said.

The researchers plan to explore the relationship between self-assembled monolayer molecule structures and perovskite precursors to identify an optimal group of self-assembled monolayer molecules for this technique, thereby enhancing the overall performance of the PSCs. The research findings were published in the journal Nature Energy.

Image caption: Perovskite solar cells fabricated by the one-step solution spin-coating method. Image credit: Dr Zhu Zonglong’s research group/City University of Hong Kong.