Electrosprayed TiO nanoporous hemispheres for enhanced electron transport and device performance of formamidinium based perovskite solar cells.

Titanium dioxide (TiO) nanoporous hemispheres (NHSs) with a radius of ∼200 nm are fabricated by electrospraying a hydrothermally synthesized TiO nanoparticle (NP) suspension solution. The resulting TiO NHSs are highly porous, which are beneficial to the infiltration of perovskites and provide a larger contact area, as building blocks to construct a mesoporous TiO layer for FAMAPb(IBr) based perovskite solar cells (PSCs). By varying the TiO NHS collecting period (15 s, 30 s, 60 s and 90 s) during the electrospraying process, the performance of PSCs changes with different TiO NHS distribution densities. The optimized PSC employing TiO NHSs (60 s) exhibits a photovoltaic conversion efficiency (PCE) as high as 19.3% with a J of 23.8 mA cm, a V of 1.14 V and a FF of 0.71. Furthermore, the PSC possesses a reproducible PCE value with little hysteresis in its current density-voltage (J-V) curves. The small perturbation transient photovoltage (TPV) measurement reveals a longer free carrier lifetime within the TiO NHS based PSC than that in the TiO NP based PSC, and the time of flight (TOF) photoconductivity measurement shows that charge mobilities in this system are also enhanced. These characteristics make TiO NHSs a promising electron transport material for efficient photovoltaic devices.