Pr3+ ions activated TiO2 nanoparticles as electron transport layer for copper based (CH3NH2)2CuBr4 perovskites solar cells

In emerging organic-inorganic perovskite solar cells (PSCs), the role of efficient electron transport layers (ETLs) is critical for electron transfer and hole blocking. TiO₂ is one of the widely reported ETLs but limits the performance of the devices exhibiting restricted electron mobility and numerous defect states. The process of doping rare earth ions has been an effective approach in improving the electronic and optical properties of TiO₂ for enhanced efficiency of PSCs. The present work studies the effect of praseodymium (Pr³⁺) doped TiO₂ prepared via sol-gel technique as electron transport layers for lead-free perovskite solar cells. The X-ray diffraction (XRD) and diffuse reflectance spectroscopy (DRS) studies showed that the crystallite size and bandgap of the particles reduced as a function of Pr³⁺ doping concentration. The X-ray photoelectron spectroscopy (XPS) analysis of the samples inferred that Pr³⁺ ions majorly remained on the TiO₂ surface. Copper-based (CH₃NH₂)₂CuBr₄ perovskites were synthesized by solution method as an active layer for the solar cells. XRD, FTIR (Fourier Transform Infrared Spectroscopy) and XPS analysis confirmed the formation of 2D-perovskite phase of the samples. The scanning electron microscopy (SEM) analysis of the perovskites revealed well crystalline orthorhombic structures. Current-voltage measurements were carried out to study better passivation properties with rare-earth doping of the ETLs and was found to be most enhanced for 0.07 Pr³⁺ concentration. Electro-chemical Impedance Spectroscopy (EIS) studies of the solar cells showed a reduced interface recombination and enhance charge transfer properties as a function of rare-earth dopant concentration. Further, the fabricated perovskite solar cells showcased better performance with xPr³⁺:TiO₂ ETLs and the maximum efficiency of ∼1.25 % was obtained for TiO₂: 0.07 Pr³⁺.