Investigation of high performance TiO₂ nanorod array perovskite solar cells

In this paper, systematic investigations on the fabrication and characterization of high performance TiO₂ nanorod array perovskite solar cells (NAPSCs) are reported. The TiO₂ nanorods, of length around 350-400 nm, were grown by solvothermal technique directly on glass/FTO substrates. From the scanning transmission electron microscopy (STEM) we demonstrate that excellent crystallinity for the TiO₂ nanorods can be produced using the solvothermal technique. Precursor consisting of a mixture of PbI₂, CH₃NH₃I (MAI) and CH₃NH₃Cl (MACl) was used for the growth of perovskite thin films on the glass/FTO/TiO₂ nanorod array (TiO₂-NA) substrates. It is found that the morphology and quality of the perovskite layer depend strongly on the concentration of MACl in the precursor. Experimental studies on femtosecond transient absorption (fs-TA) indicate that the incorporation of TiO₂-NA greatly enhances the collection efficiency of the photo-generated carriers due to substantial increase of interfacial area between the perovskite and TiO₂-NA, leading to a reduction in carrier diffusion distance. It is shown to be the key factor that the proposed technique facilitates the use of a thicker perovskite absorber layer (∼500 nm) without compromising on the series resistance. Detailed J-V characterization shows that the NAPSCs exhibit negligible hysteresis with a power conversion efficiency (PCE) >19% for the champion device.