A Facile and Green Approach to Synthesize Mesoporous Anatase TiO₂ Nanomaterials for Efficient Dye-Sensitized and Hole-Conductor-Free Perovskite Solar Cells

Mesoporous anatase TiO₂ nanomaterials (MATNs) with both large specific surface areas and structural coherence are highly desirable to achieve excellent physicochemical properties for photovoltaic applications, but the existing synthesis methods either need templates or cause pollution. Herein we report a simple, template-free, and green approach to synthesize MATNs consisting of interconnected nanoparticles. The Ti-complex intermediates were first prepared using titanium isopropoxide and acetic acid in a solvothermal reaction, which went through a morphology transformation sequence of nanowires, microspheres, and microflowers with a prolonged reaction time. Then the Ti-complex intermediates were cracked into MATNs under annealing, which were applied in dye-sensitized solar cells (DSSCs) and hole-conductor-free perovskite solar cells (HPSCs). The mesoporous anatase TiO₂ nanowire-based DSSCs achieved a high power conversion efficiency (PCE) up to 7.78% because of both a high dye-adsorption capacity and long charge-transfer channels, while the PCE based on the P25 photoelectrodes is 6.61%. The further application of mesoporous anatase TiO₂ nanowires in HPSCs achieved an improved PCE of 8.52%, compared to 6.78% for cells prepared using the P25 electrodes.