Hybrid organometal halide perovskites such as methylammonium lead iodide (MAPbI₃) are a promising class of cost- and energy-efficient light absorption materials for thin-film photovoltaics. In this work, the preparation and characterization of MAPbI₃ nanoparticles (NPs) on TiO_x/indium tin oxide glass substrates using a simple spin-coating technique have been investigated. The NPs were prepared by spin-coating solutions of MAPbI₃ and the ionic liquid (IL) 1-hexyl-3-methylimidazolium chloride in N,N-dimethylformamide. Analysis of the resulting spin-coated films revealed that uniform spherical MAPbI₃ NPs with an average diameter of 540 nm were homogeneously distributed on the TiO_x substrates. MAPbI₃ films with similar crystallinity were observed irrespective of the inclusion of IL, as evident from the X-ray diffraction patterns of the films. However, addition of IL to the spin-coating solution facilitated the formation of homogenous nucleation sites and prevented rapid crystal formation of MAPbI₃. Therefore, the presence of an IL resulted in uniform thin films with good morphology.

Perovskite solar cells (PSCs) have appeared as a promising design for next-generation thin-film photovoltaics because of their cost-efficient fabrication processes and excellent optoelectronic properties. However, PSCs containing a metal oxide compact layer (CL) suffer from poor long-term stability and performance. The quality of the underlying substrate strongly influences the growth of the perovskite layer. In turn, the perovskite film quality directly affects the efficiency and stability of the resultant PSCs. Thus, substrate modification with metal oxide CLs to produce highly efficient and stable PSCs has drawn attention. In this review, metal oxide-based electron transport layers (ETLs) used in PSCs and their systemic modification are reviewed. The roles of ETLs in the design and fabrication of efficient and stable PSCs are also discussed. This review will guide the further development of perovskite films with larger grains, higher crystallinity, and more homogeneous morphology, which correlate to higher stable PSC performance. The challenges and future research directions for PSCs containing compact ETLs are also described with the goal of improving their sustainability to reach new heights of clean energy production.

Vacuum deposition is a simple and controllable approach that aims to form higher-quality perovskite films compared with those formed using solution-based deposition processes. Herein, we demonstrate a novel method to promote the intercalation control of inorganic cesium lead iodide (CsPbI₃) perovskite thin films via alternate vacuum deposition. We also investigated the effect of layer-by-layer deposition of PbI₂/CsI to fabricate efficient planar heterojunction CsPbI₃ thin films and solar cells. This procedure is comparatively simple when compared with commonly used coevaporation techniques; further, precise intercalation control of the CsPbI₃ thin films can be achieved by increasing the number of layers in the layer-by-layer deposition of PbI₂/CsI. The best control and the highest reproducibility were achieved for the deposition of four double layers owing to the precise intercalation control during the deposition of the CsPbI₃ thin film. A power conversion efficiency of 6.79% was obtained via alternating vacuum deposition of two double layers with a short-circuit current density (J_sc) of 12.06 mA/cm², an open-circuit voltage (V_oc) of 0.79 V, and a fill factor (FF) of 0.72. Our results suggest a route for inorganic precursors to be used for efficient perovskite solar cells via alternating vacuum deposition.

We demonstrate phase separation of co-evaporated zinc phthalocyanine (ZnPc) and fullerene (C₆₀) for efficient organic photovoltaic cells. With introducing a poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) film and a crystalline copper iodide film on indium tin oxide, 20-nm-thick ZnPc film adopts a lying-down crystalline geometry with grain sizes of about 50 nm. This surface distributed with strong interaction areas and weak interaction areas enables the selective growth of ZnPc and C₆₀ molecules during following co-evaporation, which not only results in a phase separation but also improve the crystalline growth of C₆₀. This blend film greatly enhances the efficiencies in photocurrent generation and carrier transport, resulting in a high power conversion efficiency of 4.56% under 1 sun.

Cesium iodide (CsI) is attracting attention as a substitute for organic materials such as CH ₃ NH ₃ I. In this work, we fabricated sequential-vacuum-deposited planar heterojunction (PHJ) cesium lead iodide (CsPbI ₃ ) perovskite solar cells with enhanced efficiencies by varying the annealing time (0.5, 1, 5, and 10 min). The effect of performance enhancement was investigated as a function of varying annealing time at 350 °C employing a hot plate. The best-performing device was obtained with an annealing time of 1 min, delivered photocurrent density ( J _SC ) of 12.06 mA/cm ² , voltage ( V _OC ) of 0.71 V, and fill factor (FF) of 0.67, leading to a power conversion efficiency (PCE) of 5.71% at standard AM 1.5G solar illumination.