Morphology control by optimizing process conditions for efficient wide-bandgap perovskite solar cells

Efficient wide-bandgap perovskite is essential to construct the tandem structure to achieve efficiency beyond the Shockley-Queisser limit of single-junction solar cells. But the performance of wide-bandgap perovskites is mostly limited by the defects in the Br-rich active layer. Morphology, especially the grain boundaries, roughness, unreacted lead halides, etc. play important role in regulating the defects. Here, we report an efficient way to control the morphology and properties of the perovskite by adjusting process temperature (glove box temperature) during crystallization and tailoring the annealing process. It was observed that GB temperature maintained at ~27 °C with a delay before annealing results in bigger grains and less unreacted lead halides with a more uniform and smoother perovskite film, which results in reduced defects and better charge transport properties. The synergy of these two led to an efficiency of 15.68% for 1.78 eV perovskite solar cells compared to 12.53% of that without adjustment of the process conditions. The findings of this work offer a new window to optimize the morphology of the perovskite for higher efficiency and stability.