Multi-step slow annealing perovskite films for high performance planar perovskite solar cells

•Perovskite films treated by two annealing methods were compared.•Annealing temperature and duration greatly affected perovskite films.•Slow annealing resulted in high-efficient perovskite solar cells.•The slow annealing device showed the best efficiency of 13.58%.

The morphology, structure, optical and electrical properties of perovskite films treated by two different annealing methods with different annealing temperature ramp and their corresponding device performance have been studied and compared. Annealing temperature ramp significantly influences the surface morphology and optical properties of perovskite films which determines the performance of solar cells which determines the performance of solar cells. The perovskite films treated by one-step direct annealing method tend to exhibit irregular and weak ultraviolet–visible absorption spectrum, which can easily result in great variation in the final performance of solar cells. While multi-step slow annealing is beneficial for preparing highly uniform and well-crystallized perovskite films, and thus these devices present tightly-distributed performance parameters. The best device treated by multi-step slow annealing method showed a short circuit current density of 21.49 mA/cm2, an open circuit voltage of 0.988 V, a fill factor of 64.86%, and a power conversion efficiency (PCE) of 13.58%, which is a 57% enhancement of the overall PCE relative to 8.65% of the device treated by one-step annealing method. These findings suggest that optimized slow temperature ramp is necessary to prepare high-efficient and well-reproducible perovskite solar cells.

Graphical abstractIn this article, multi-step slow annealing is adopted for preparing highly uniform perovskite films and high-efficient and well-reproducible planar perovskite solar cells that present tightly-distributed performance parameters.Figure optionsDownload full-size imageDownload as PowerPoint slide