Hollow Rice Grain-Shaped TiO2 Nanostructures for High-Efficiency and Large-Area Perovskite Solar Cells

Hollow rice grain-shaped titanium dioxide (TiO2) nanostructures (NSs) with the radius of 200-300 nm are fabricated by electrospinning titanium isopropoxide solution and further calcination. The resulting hollow rice grain-shaped TiO2 NSs are highly porous, which are beneficial to the infiltration of perovskites and provide a large contact area, as the building blocks to construct the mesoporous TiO2 layer for the large-area (the active area is 1 cm(2)) CH3NH3PbI3 based perovskite solar cells (PSCs). By varying the spin coating speed (2000 rpm, 4000 rpm, and 8000 rpm, respectively), the performance of PSCs changes with different TiO2 NSs distribution densities. The optimized PSC employing the 4000 rpm spin coating speed exhibits a photovoltaic conversion efficiency (PCE) of 14.2% with the short circuit current density (J(sc)) of 21.6 mA cm(-2), open circuit voltage (V-oc) of 1.07 V and fill factor (FF) of 0.61, which is superior to the plain structure based control group with the PCE of 9.6%. Furthermore, the PSC possesses a reproducible PCE value with weak hysteresis in its current density voltage (J-V) curves. Moreover, photoluminescence (PL) measurements and finite-difference time-domain (FDTD) optical simulations reveal the enhanced fast charge carrier extraction/transport and light absorption in the proposed system, which makes electrospun hollow rice grain-shaped TiO2 NSs a promising electron transportation material for high-efficiency and large-area photovoltaic devices.