The 1.68-1.73 eV bandgap inorganic perovskite has excellent photovoltaic and thermal stability, and there is almost no risk of phase separation. It is one of the excellent top cell candidates for tandem solar cells (TSCs). However, the extremely serious non-radiative recombination within inorganic perovskite solar cells (IPSCs) severely restricts the improvement of the PCE of single-junction and TSCs devices. Studies have shown that the defect density on the surface of perovskite solar cells is three orders of magnitude higher than that within the material. Therefore, the rational regulation of the defect density on the surface is indispensable for enhancing the performance of photovoltaic devices.

This paper utilizes the dual (pentafluorobenzene) zinc (B(PFP)Zn) to manage the interface defect density between the photoabsorption layer and the ETL. After the B(PFP)Zn treatment, the device defect density has decreased from 1.63×10¹⁶ cm³ to 1.32×10¹⁶ cm³. Based on this, the PCE of the inverse-type devices fabricated by air was significantly enhanced from 16.07% to 18.72%. Both humidity and thermal stability were improved to a considerable extent.

The diffraction peaks of the inorganic perovskite corresponding to the B(PFP)Zn treatment have been enhanced. This is because B(PFP)Zn interacts with the inorganic perovskite during the secondary annealing process, thereby achieving recrystallization. Observe the surface morphology of the films before and after B(PFP)Zn treatment by means of SEM. SEM images indicate that the surface pores of the films treated with B(PFP)Zn are reduced. The surface morphology of the film was analyzed by using atomic force microscopy (AFM), the surface roughness of the film treated with B(PFP)Zn was reduced. After the B(PFP)Zn interface treatment, the PCE of the device was significantly enhanced from 16.07% to 18.72%. The average open-circuit voltage (V_OC) of the devices increased by 70 mV, and the average FF increased from 77% to 81%.

The films treated by B(PFP)Zn surface treatment have higher PL intensity and the carrier lifetime is nearly twice that of the reference group films, indicating that the defect density at the perovskite/ETL interface has decreased and non-radiative recombination has been suppressed. The devices treated with B(PFP)Zn exhibit lower leakage current. Carry out the space charge limited current (SCLC) tests on the two devices by using the pure hole devices, after the B(PFP)Zn surface treatment, the defect density decreased from 1.63×10¹⁶ cm³ to 1.32×10¹⁶ cm³.

The humidity stability of the two devices was monitored in an environment with 20% to 30% humidity, the PCE of the reference group devices dropped to 80% of the initial value at 115 h, while that of the experimental group dropped to the same level at approximately 300 h.

In this paper, B(PFP)Zn was utilized to perform post-treatment on the surface of CsPbI_2.85Br_0.15 film. The recrystallization process enhanced the crystallization quality of the film, effectively reduced the defect density, to some extent suppressed non-radiative recombination, and decreased the accumulation of charge carriers at the interface. The inverse-phase IPSCs prepared based on air achieved a record PCE of 18.72%, with an average V_OC increase of up to 70 mV. This strategy is simple and highly repeatable, providing a new scientific idea and technical route for the transformation and upgrading of the photovoltaic industry.