Chen Weijie

Due to its super thermal stability, inorganic CsPbI₂Br perovskite has attracted more and more attention in the field of photovoltaic application. However, its device performance, as reported to date, is greatly challenged in preparing CsPbI₂Br films with both sufficient absorbance and high quality. Herein, crystallization engineering is applied in producing solution-processed CsPbI₂Br film to guarantee sufficient light harvesting and effective carrier extraction. Further study proves that the precursor solution temperature would largely affect the crystallization progress: (1) the nucleation step is highly related to the solubility of precursor in a specific solvent or solvents at elevated temperatures; (2) the crystal growth rate is highly related to the solvent evaporation rate. To obtain thick film with larger crystalline grain size, the precursor solution temperature should be carefully adjusted for both suppressing the formation of too many nuclei and increasing the crystallization rate at the same time. Finally, the optimized CsPbI₂Br would be obtained when the precursor solution is maintained at 100 °C, the corresponding device shows a stabilized efficiency as high as 14.81%. As far as we know, this is the highest PCE for the CsPbBrI₂ perovskite based solar cells.

Herein, the correlation between crystallization and external factors (solubility and solvent evaporation rate) is conducted for solution-processed CsPbI₂Br film. With moderate precursor solution temperature, homogenous, pinhole-free, large crystalline grain size and thick CsPbI₂Br film was obtained, which effectively increased the light absorption, and decreased recombination loss. As a result, the optimized champion device achieved long-term stabilized PCE of 14.81%.

Advancing perovskite solar cell (PVSC) technologies toward its theoretical power conversion efficiency (PCE) and optimum stability requires stringent control over interfacial trap densities in the devices. By introducing a new macromolecular interlayer material of PPDIN6 at the PCBM/Ag interface for planar p-i-n PVSCs, we succeeded in significantly reducing the trap density, thereby facilitating electron extraction and suppressing electron recombination at the interface. Consequently, a PCE of 20.43% was achieved with a record fill factor of 83.4%, which is one of the highest values for planar p-i-n PVSCs. Moreover, the amine groups in PPDIN6 could neutralize the migrating iodide ions and thus inhibit the formation of the insulating Ag–I bonds on the surface of the Ag electrode. As a result, we realized long-term stability for PPDIN6 based PVSCs, which maintained 85% of their initial performance after continuous operation at their maximum power point for 200 h under 1-sun illumination in air with a relative humidity of 30–50%.