Electrosprayed TiO₂ nanoporous hemispheres for enhanced electron transport and device performance of formamidinium...

Titanium dioxide (TiO₂) nanoporous hemispheres (NHSs) with a radius of ∼200 nm are fabricated by electrospraying a hydrothermally synthesized TiO₂ nanoparticle (NP) suspension solution. The resulting TiO₂ 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 TiO₂ layer for FA_0.81MA_0.15Pb(I_0.836Br_0.15)₃ based perovskite solar cells (PSCs). By varying the TiO₂ NHS collecting period (15 s, 30 s, 60 s and 90 s) during the electrospraying process, the performance of PSCs changes with different TiO₂ NHS distribution densities. The optimized PSC employing TiO₂ NHSs (60 s) exhibits a photovoltaic conversion efficiency (PCE) as high as 19.3% with a J_sc of 23.8 mA cm^-2, a V_oc 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 TiO₂ NHS based PSC than that in the TiO₂ NP based PSC, and the time of flight (TOF) photoconductivity measurement shows that charge mobilities in this system are also enhanced. These characteristics make TiO₂ NHSs a promising electron transport material for efficient photovoltaic devices.