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

A HC(NH₂)₂PbI₃ 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)₂PbI₃ 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)₂PbI₃ 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.