Opto-electronic properties of TiO2 nanohelices with embedded HC(NH2)(2)PbI3 perovskite solar cells

A HC(NH2)(2)PbI3 solar cell of perovskite structure based on TiO2 nanohelices has been developed. Well-aligned helical TiO2 arrays of different pitch (p) and radius (r), helix-1 (p/2 = 118 nm, r = 42 nm), helix-2 (p/2 = 353 nm, r = 88 nm) and helix-3 (p/2 = 468 nm, r = 122 nm), were grown on fluorine-doped tin oxide (FTO) glass by oblique-angle electron beam evaporation. HC(NH2)(2)PbI3 perovskite was deposited on the TiO2 nanohelices by a two-step dipping method. Helix-1 showed higher short-circuit current density (J(SC)), whereas helix-3 exhibited slightly higher open-circuit voltage (V-OC). HC(NH2)(2)PbI3 perovskite combined with helix-1 demonstrated an average power conversion efficiency of 12.03 +/- 0.07% due to its higher J(SC) compared to helix-2 and helix-3. The higher J(SC) of helix-1 could be attributed to its greater light scattering efficiency and higher absorbed photon-to-current conversion efficiency. In addition, despite having the longest pathway structure, helix-1 showed rapid electron diffusion, attributed to its higher charge injection efficiency due to the larger contact area between perovskite and TiO2. We have established that fine tuning of the interface between perovskite and the electron-injecting oxide is a crucial factor in achieving a perovskite solar cell of high performance.