A review of experimental and computational attempts to remedy stability issues of perovskite solar cells

Photovoltaic technology using perovskite solar cells has emerged as a potential solution in the photovoltaic makings for cost-effective manufacturing solutions deposition/coating solar cells. The hybrid perovskite-based materials possess a unique blend from low bulk snare concentrations, ambipolar, broad optical absorption properties, extended charge carrier diffusion, and charge transport/collection properties, making them favourable for solar cell applications. However, perovskite solar cells devices suffer from the effects of natural instability, leading to their rapid degradation while bared to water, oxygen, as well as ultraviolet rays, are irradiated and in case of high temperatures. It is essential to shield the perovskite film from damage, extend lifetime, and make it suitable for device fabrications. This paper focuses on various device strategies and computational attempts to address perovskite-based solar cells' environmental stability issues.

A Study on the Effect of Ambient Air Plasma Treatment on the Properties of Methylammonium Lead Halide Perovskite Films

Organic-inorganic halide perovskite materials are considered excellent active layers in the fabrication of highly efficient and low-cost photovoltaic devices. This contribution demonstrates that rapid and low-temperature air-plasma treatment of mixed organic-inorganic halide perovskite film is a promising technique, controlling its opto-electrical surface properties by changing the ratio of organic-to-inorganic components. Plasma treatment of perovskite films was performed with high power-density (25 kW/m2 and 100 W/cm3) diffuse coplanar surface barrier discharge (DCSBD) at 70 °C in ambient air. The results show that short plasma treatment time (1 s, 2 s, and 5 s) led to a relatively enlargement of grain size, however, longer plasma treatment time (10 s and 20 s) led to an etching of the surface. The band-gap energy of the perovskite films was related to the duration of plasma treatment; short periods (≤5 s) led to a widening of the band gap from ~1.66 to 1.73 eV, while longer exposure (>5 s) led to a narrowing of the band gap to approx. 1.63 eV and fast degradation of the film due to etching. Surface analysis demonstrated that the film became homogeneous, with highly oriented crystals, after short plasma treatment; however, prolonging the plasma treatment led to morphological disorders and partial etching of the surface. The plasma treatment approach presented herein addresses important challenges in current perovskite solar cells: tuning the optoelectronic properties and manufacturing homogeneous perovskite films.

Growth of Compact CH3NH3PbI3 Thin Films Governed by the Crystallization in PbI2 Matrix for Efficient Planar Perovskite Solar Cells

As a convenient preparation technique, a two-step method, which is normally done by spin-coating CH₃NH₃I onto PbI₂ film followed by a thermal annealing, is generally used to prepare solution-processed CH₃NH₃PbI₃ films for planar perovskite solar cells. Here, we prepare the compact CH₃NH₃PbI₃ thin films by the two-step method at a low temperature (<80 °C) and investigate the effects of PbI₂ crystallization on the structure-property correlation in the CH₃NH₃PbI₃ films. It is found that the importance of the crystallization in PbI₂ matrix lies in governing the transition from the (001) plane of trigonal PbI₂ to the (002) plane of tetragonal CH₃NH₃PbI₃ in the rapid reaction process for atoms to coordinate into perovskite during spin-coating, which actually determines the morphology and the type of vacancy defects in resulting perovskite; a better crystallized PbI₂ film has a much stronger ability to react with CH₃NH₃I solution and produces larger CH₃NH₃PbI₃ grains with a higher crystallinity. The CH₃NH₃PbI₃/TiO₂ planar solar cell derived from a better crystallized PbI₂ film exhibits significantly improved performance and stability as the result of the higher crystallinity inside the perovskite film. Moreover, it is demonstrated that the crystalline PbI₂ film matrix subjected to the annealing after a slow heating process prior to contacting CH₃NH₃I solution is more effective for CH₃NH₃PbI₃ formation than that with a direct annealing history. The results in this paper provide a guide for preparing high-quality CH₃NH₃PbI₃ thin films for efficient perovskite solar cells and CH₃NH₃PbI₃ interfacial films over the layers susceptible to temperature.

WO3 Nanoparticles or Nanorods Incorporating Cs2CO3/PCBM Buffer Bilayer as Carriers Transporting Materials for Perovskite Solar Cells

In this work, we demonstrate a novel carrier transporting combination made of tungsten trioxide (WO₃) nanomaterials and Cs₂CO₃/PCBM buffer bilayer for the fabrication of perovskite solar cells (PSCs). Two different types of WO₃, including nanoparticles and nanorods, were prepared by sol-gel process and hydrothermal method, respectively. Cs₂CO₃/PCBM buffer bilayer was inserted between WO₃ and perovskite layers to improve charge transfer efficiency and formation of pinhole-free perovskite layer. Besides, the leakage current of the devices containing Cs₂CO₃/PCBM buffer bilayer was significantly suppressed. The optimized device based on WO₃ nanoparticles and Cs₂CO₃/PCBM bilayer showed an open-circuit voltage of 0.84 V, a short-circuit current density of 20.40 mA/cm², a fill factor of 0.61, and a power conversion efficiency of 10.49 %, which were significantly higher than those of PSCs without Cs₂CO₃/PCBM buffer bilayer. The results revealed that the combination of WO₃ nanomaterials and Cs₂CO₃/PCBM bilayer provides an effective solution for improving performances of PSCs.