The investigation of crystal growth is crucial for us to improve the film quality and photophysical properties of CH₃NH₃PbI₃ (MAPbI₃). In the two-step spin-coating process, the crystal structure could be modulated by controlling the growth conditions of PbI₂ and CH₃NH₃I (MAI) layers. In this paper, the PbI₂ layer was treated with annealing under different times. A liquid–liquid diffusion (LLD) mechanism is proposed to modify the deposition of MAI precursor solution and enhance the flatness of organic–inorganic hybrid perovskite film. Furthermore, the perovskite films are prepared using different concentrations of MAI. The evolution process of perovskite structure is observed by modulating the concentration of MAI. The spin-coating of moderate MAI tends to form high quality MAPbI₃ films with enhanced absorption and carrier extraction capabilities. The high concentration of MAI would cause the perovskite phase transition, which provides a novel perspective to modulate the structure of organic–inorganic hybrid perovskite in the two-step spin-coating process, although it deteriorates the device performance.

It is crucial to find a good material as a hole transport layer (HTL) to improve the performance of perovskite solar cells (PSCs), devices with an inverted structure. Polyethylene dioxythiophene-poly (styrene sulfonate) (PEDOT:PSS) and inorganic nickel oxide (NiO_x) have become hotspots in the study of hole transport materials in PSCs on account of their excellent properties. In our research, NiO_x and PEDOT: PSS, two kinds of hole transport materials, were prepared and compared to study the impact of the bottom layer on the light absorption and morphology of perovskite layer. By the way, some experimental parameters are simulated by wx Analysis of Microelectronic and Photonic Structures (wxAMPS). In addition, thin interfacial layers with deep capture levels and high capture cross sections were inserted to simulate the degradation of the interface between light absorption layer and PEDOT:PSS. This work realizes the combination of experiment and simulation. Exploring the mechanism of the influence of functional layer parameters plays a vital part in the performance of devices by establishing the system design. It can be found that the perovskite film growing on NiO_x has a stronger light absorption capacity, which makes the best open-circuit voltage of 0.98 V, short-circuit current density of 24.55 mA/cm², and power conversion efficiency of 20.01%.

The depolarization field of ferroelectric photovoltaic materials can enhance the separation and transport of photogenerated carriers, which will improve the performance of photovoltaic devices, thus attracting the attention of researchers. In this paper, a narrow bandgap molecular ferroelectric Hexane-1,6-diammonium pentaiodobismuth (HDA-BiI₅) was selected as the photo absorption layer for the fabrication of solar cells. After optimizing the ferroelectric thin film by the antisolvent process, the effect of different polarization voltages on the performance of ferroelectric devices was studied. The results showed that there was a significant increase in short-circuit current density, and the photoelectric conversion efficiency showed an overall increasing trend. Finally, we analyzed the internal mechanism of the effect of polarization on the device.

The rapidly developing organic–inorganic hybrid chalcogenide solar cells have now become a hot topic of interest. However, the bandgap of inorganic ferroelectric materials with a typical chalcogenide structure is too wide to match the solar spectrum, while the ferroelectricity of organic-inorganic hybrid chalcogenide materials with a narrow bandgap, meth amide–lead–iodine, is not obvious, and the lead element causes environmental pollution. The recently discovered organic–inorganic hybrid material [C₆N₂H₁₈]BiI₅ with good ferroelectricity and the narrowest bandgap of molecular ferroelectrics can absorb visible light in the range of 380 nm to 660 nm, and compound [C₆N₂H₁₈]SbI₅ with the Bi cognate element Sb was also synthesized. In this paper, we designed the first experiment to prepare thin films by mixing and doping the above two materials in five different molar ratios, and we comparatively studied the changes in crystal structure, surface morphology, and photophysical properties of the prepared multicomponent hybrid films according to the mixing ratio. A theoretical model was developed to calculate and analyze the bandgap of the hybrid doped compounds and compare it with the experimental values. It was found that the absorption spectra of the multicomponent hybrid films were red-shifted relative to the original material, indicating that the forbidden bandwidth was reduced to absorb a wider range of visible light, and the reason for this was thought to be the narrowing of the bandgap due to doping. When the mixing ratio was 0.4:0.6, the bandgap was the narrowest and the light absorption was the best; the highest quality of the film was obtained when the mixing ratio was 0.5:0.5.