Complete coverage of perovskite materials over ZnO Nanorods with Multiwalled Carbon Nanotubes (MWCNTs) as Hole Transport Material (HTM)

In this research, ZnO nanorods (NRs) have been fabricated for perovskite solar cell (PSC) application. An issue about the use of ZnO material for PSC application is lower photovoltaic outputs than TiO₂ material. Such outcome is due to unstable ZnO/perovskite interface. Other factor is due to partial coverage of the perovskite over the ZnO material. By using 1-step method and mixture of DMF and DMSO as the solvent for perovskite solution, complete coverage of the ZnO NR was achieved. Multiwalled carbon nanotubes (MWCNTs) and copper iodide (CuI) were used as hole transport materials (HTMs) for comparison purpose. The experiment and characterization were done in Shizuoka University, Hamamatsu campus, Japan. The ZnO NRs were grown by implementing 2-steps method of seed layer deposition by spin coating and NRs growth through chemical bath deposition. Methylammonium lead iodide (CH₃NH₃PbI₃ or MAPbI₃) perovskite was grown through 1-step method by mixing equimolar lead iodide (PbI₂) and methylammonium iodide (CH₃NH₃I or MAI) in DMF and DMSO solvents (volume ratio of 7 to 1 for DMF and DMSO, respectively). The current-voltage (I-V) curve for both materials showed higher J_SC and V_OC for MWCNTs at 5.34 mA/cm² and 0.21 V, respectively compared to CuI materials (J_SC = 3.40 mA/cm² and V_OC = 0.14 V). Lower V_OC is the result of higher series resistance due to non-passivated ZnO/MAPbI3 interface. Another factor to consider is recombination of electron and hole at the interface. MWCNT material is an alternative material to act as HTM because of high conductivity and lower electrical resistance compared to CuI. Complete coverage of the perovskite over ZnO material helped improving the production of photogenerated electrons.