The hole blocking layer plays an important role in suppressing recombination of holes and electrons between the perovskite layer and fluorine-doped tin oxide (FTO). Morphological defects, such as cracks, at the compact TiO₂ hole blocking layer due to rough FTO surface seriously affect performance of perovskite solar cells (PSCs). Herein, we employ a simple spin-coating SnO₂ thin film solution to cover cracks of TiO₂ hole blocking layer for PSCs. The experiment results indicate that the TiO₂/SnO₂ complementary composite hole blocking layer could eliminate the serious electrical current leakage existing inside the device, extremely reducing interface defects and hysteresis. Furthermore, a high efficiency of 13.52% was achieved for the device, which is the highest efficiency ever recorded in PSCs with spongy carbon film deposited on a separated FTO-substrate as composite counter electrode under one sun illumination.

High-performance perovskite solar cells are strongly dependent on the quality of the perovskite layer. Two-step sequential deposition of CH₃NH₃PbI₃ (MAPbI₃) films is widely used to fabricate perovskite solar cells and many factors influence the quality of perovskite films, such as the delay time before annealing the MAI-PbI₂-DMSO intermediate phase, which would impact the morphology and photo-physical properties of perovskite thin films. Here, the experimental research indicates that the impact of the delay time before annealing the MAI-PbI₂-DMSO intermediate phase on the quality, crystallinity, and photo-physical properties of perovskite film is crucial. During the delay process, the delay time before annealing the MAI-PbI₂-DMSO intermediate phase plays an important role in the nucleation process of perovskite grains inside the intermediate phase. With the extension of the delay time before annealing, the quality of the perovskite film deteriorates, thus the photo-physical properties change. We found that after the localized liquid–liquid diffusion of MAI and PbI₂, with the extension of the delay time before annealing the MAI-PbI₂-DMSO intermediate phase, the nucleation number of the perovskite grains increases and the grain size becomes smaller. Therefore, with the extension of the delay time before annealing, the device performance deteriorates.

Perovskite thin films with excellent optical semiconductor and crystallization properties and superior surface morphology are normally considered to be vital to perovskite solar cells (PSCs). In this paper, we systematically survey the process of modulating surface morphology and optical semiconductor and crystallization properties of methylammonium lead iodide film by controlling doping of K⁺ for PSC prepared in air and propose the mechanism of large K⁺-doped perovskite grain formation related to crystallization speed. The increase in the crystallization speed leads to the production of large grains without localized-solvent-vapor (LSV) pores via moderate doping of K⁺, and the exorbitant crystallization speed induces super large grains with LSV pores via excessive doping of K⁺. Furthermore, the semiconductor properties (absorption band edge wavelength, PL emission peak wavelength, energy band gap) of perovskite film can be significantly tuned by controlled doping of K⁺. The investigation of the detailed process of modulating surface morphology and semiconductor properties of perovskite thin film by controlled doping of K⁺ may provide guidance and pave the way for superior component design of absorption materials for cost-efficient PSCs.

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%.