We report on the fabrication and opto-electronic characterization of solution-processed planar heterojunction perovskite solar cells based on methylammonium (MA) lead halide derivatives, MAPbI _3−x Y _x (Y = Cl, Br, I).

In this work, TiO₂ nanoparticles (NPs) were effectively synthesized by a green method using the Impatiens rothii Hook.f. leaf (IL) extract as a capping and reducing agent. The as-synthesized TiO₂ NPs were characterized by different characterization methods such as the Brunauer-Emmett-Teller (BET) analysis, high-resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), diffused reflectance spectroscopy (DRS), and X-ray diffraction (XRD) and Raman spectroscopy. The specific surface area from BET analysis was found to be 65 m²/g. The average crystallite size from XRD analysis and average particle size from SEM analysis were found to be ∼11 and ∼25 nm, respectively. The Raman spectroscopy and XRD results showed that the biosynthesized (IL-TiO₂) nanoparticles were purely anatase phase. XPS analysis illustrated the formation of Titania with an oxidation state of +4. The DRS study showcased that a blue-shifted intense absorption peak of IL-TiO₂ (3.39 eV) compared to the bulk material reported in the literature (3.2 eV). HRTEM micrograph showed the presence of grain boundary with d spacings of 0.352, 0.245, and 0.190, which correspond to the lattice planes of (101), (004), and (200), respectively. From the EDX analysis, the weight percents of titanium and oxygen were found to be 54.33 and 45.67%, respectively. The photoinduced degradation of methylene blue (MB) dye was investigated in the presence of biosynthesized IL-TiO₂ NPs photocatalyst. The effect of parameters like catalyst dosage (30 mg/L), initial concentration of MB (15 ppm), pH (10.5), and contact time (100 min) on the removal efficiency was optimized. The maximum photodegradation efficiency under the optimized conditions was found to be 98%.

Outstanding improvement in power conversion efficiency (PCE) over 25% in a very short period and promising research developments to reach the theoretical PCE limit of single junction solar cells, 33%, enables organic–inorganic perovskite solar cells (OIPSCs) to gain much attention in the scientific and industrial community. The simplicity of production of OIPSCs from precursor solution either on rigid or flexible substrates makes them even more attractive for low-cost roll-to-roll production processes. Though OIPSCs show as such higher PCE with simple solution processing methods, there are still unresolved issues, while attempts are made to commercialize these solar cells. Among the major problems is the instability of the photoactive layer of OIPSCs at the interface of the charge transport layers and /or electrodes during prolonged exposure to moisture, heat and radiation. To achieve matched PCE and stability, several techniques such as molecular and interfacial engineering of components in OIPSCs have been applied. Moreover, in recent times, engineering on additives, solvents, surface passivation, and structural tuning have been developed to reduce defects and large grain boundaries from the surface and/or interface of organic–inorganic perovskite films. Under this review, we have shown recently developed additives and passivation strategies, which are strongly focused to enhance PCE and long-term stability simultaneously.