The influence of metal oxide transport layer and annealing temperature on perovskite solar cells (PSCs)

Abstract

Organic-inorganic halide Perovskite Solar Cells (PSCs) are the leading third-generation solar cells with the possibility to provide a fraction of green and affordable energy in the next technological era of solar energy. This type of photovoltaic cell is still new and has recently gained interest due to its low production cost, easy fabrication and rapidly improving power conversion efficiency (PCE). The performance of PSCs depends on the metal oxide/perovskite interface. This work focuses on improving the intermediate contact between the light-active perovskite layer and the electron transport layer (ETL) in a fully ambient PSC by annealing titanium dioxide (TiO2) ETL at extreme temperatures. The TiO2 semiconducting material was successfully synthesized using the hydrothermal method due to the method’s ability to produce pure and crystalline nanoparticles at low temperatures. With the future application of TiO2 projected to flexible conductive substrates, the as-synthesized TiO2 nanopowders were preheated from 200 to 1200 ℃ temperature range prior to deposition to avoid substrate deformation. To investigate the effect of annealing on the synthesized TiO2 nanopowders X-ray diffraction (XRD), transmission electron microscopy (TEM), Scanning electron microscopy (SEM), Energy dispersive x-ray (EDX) spectroscopy, Fourier transform infrared spectroscopy (FT-IR), and Ultraviolet-visible spectroscopy (UV-Vis) techniques were employed to study the structural, morphological, and opto-chemical property changes according to the temperature range described. From the crystal and morphology analysis, the as-synthesized TiO2 nanomaterial appears to be a crystalline multiphase material showing coexistence of anatase and rutile phases. Annealing increases the metal oxide crystallinity, porosity, and particle dispersion. The optical analysis of TiO2 material reveals successful bandgap tuning of the metal oxide wide-bandgap structure. The perovskite active layer was formed through the two-step spin coating of lead iodide (PbI2) and methylammonium iodide (CH3NH3I) respectively. To investigate the morphological structure, thermal and optical properties of TiO2/CH3NH3PbI3 SEM, Thermogravimetric analysis (TGA), Photoluminescence spectroscopy (PL), and UV-Vis techniques were used. Finally, perovskite solar cells of device structure ITO/c-TiO2/m-TiO2/MAPbI3/Spiro-MeoTAD/Conductive Ag ink/ITO were fabricated and their performance was evaluated using the Keithley solar simulator.