Perovskites are promising materials for next-generation solar cells. Perovskite solar cells are cheap to produce and could be used in flexible devices. Their efficiency has increased significantly over the last decade. However, the use of perovskite solar cells is still hampered by their lack of long-term stability and difficulties with upscaling.

Yabing Qi, Okinawa Institute of Science and Technology Graduate University (OIST), Japan, and colleagues have developed a strategy to fabricate large‐area uniform perovskite films with a thickness of over one micrometer. The team used a PbI₂ precursor solution in dimethylformamide (DMF). A high concentration is needed to create the desired thick perovskite layer. However, the solubility of PbI₂ in DMF makes it difficult to achieve the required concentration, and the crystallization step is difficult to control. This leads to thick films with many small grains, and thus, many grain boundaries.

To solve these issues, the team introduced NH₄Cl as an additive to increase the solubility of PbI₂. This resulted in more uniform perovskite films with much larger grains and fewer defects. Solar modules using these films with sizes of 5×5 cm² showed an efficiency of 14.55 % and retained more than 80 % of this efficiency after 1,600 h. Larger 10×10 cm² modules had an efficiency of 10.25 % and retained 80 % efficiency for over 1,100 hours.

• Scalable Fabrication of >90 cm² Perovskite Solar Modules with >1000 h Operational Stability Based on the Intermediate Phase Strategy,
  Guoqing Tong, Dae‐Yong Son, Luis K. Ono, Yuqiang Liu, Yanqiang Hu, Hui Zhang, Afshan Jamshaid, Longbin Qiu, Zonghao Liu, Yabing Qi,
  Adv. Energy Mater. 2021.
  https://doi.org/10.1002/aenm.202003712