HC(NH2)2PbI3 Perovskite Solar Cells Based on TiO2 Nanohelices

Nam-Gyu Park^a, Hyun-Seok Ko^a, Jin-Wook Lee^a, Seung Hee Lee^b, Jong Kyu Kim^b

^aSungkyunkwan University, South Korea, 300 Cheoncheon-dong, Jangan-gu, Suwon, 440, Korea, Republic of

^bDepartment of Materials Science and Engineering, Pohang University of Science and Technology, Pohang, 790-784

International Conference on Hybrid and Organic Photovoltaics
Proceedings of International Conference on Hybrid and Organic Photovoltaics 2015 (HOPV15)

Roma, Italy, 2015 May 11th - 13th

Organizer: Filippo De Angelis

Poster, Jin-Wook Lee, 061
Publication date: 5th February 2015

400 nm-thick TiO₂ nanohelices with 63% porosity were grown on fluorine-doped tin oxide (FTO) glass via oblique-angle electron beam evaporation, in which pitch (p) and radius (r) of the helices were varied. Pitch and radius of 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 determined from cross-sectional scanning electron microscopy (SEM) images. HC(NH₂)₂PbI₃ with 150 nm-thick capping layer was formed on the helical TiO₂ arrays using two-step dipping method, in which spiro-MeOTAD was used as a hole transporting material. Perovskite solar cell incorporating helix-1 and helix-3 show higher average short-circuit current density (J_SC) of 19.88±0.15 mA/cm²). Light harvesting efficiency and adsorbed photon-to-electron conversion efficiency measurement confirm that higher J_SCs from helix-1 and helix-3 partially result from higher light scattering while it is mainly due to higher charge injection and/or collection efficiency. Time-resolved photocurrent response enables qualitative comparison of the amount of electrons transporting through helical TiO₂ (slow responding component, rise time>0.02 s) and perovskite it self (fast responding component, rise time<0.002 s). Helix-1 shows higher portion of electrons transporting through helical TiO₂, and helix-3 and helix-2 are followed while opposite tendency is observed for electrons transporting through perovskite. Higher portion of electrons injected to helix-1 is attributed to higher contact area between helical TiO₂ and perovskite as estimated by 3D modeling (helix-1:helix-2:helix-3=1.17:1.00:1.08). Finally, transient photocurrent decay measurement elucidates that diffusion coefficient (7.38x10^-6 cm²s^-1 for helix-1, 2.88x10^-6 cm²s^-1 for helix-2 and 4.90x10^-6 cm²s^-1) resulting from higher amount of electrons injected to helical TiO₂.

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