2D homologous organic-inorganic hybrids as light-absorbers for planer and nanorod-based perovskite solar cells

We present the fabrication and characterization of two dimensional (2D) perovskites (PEA)2(MA)m-1PbmI3 m+1 (PEA=phenylethylammonium, MA=methylammonium, m=1,2,3) for application as light absorbers in solar cells. Films of 2D perovskite series show high stability under humid air, with band gaps decreasing with increasing m values, from 2.36 eV for (PEA)2PbI4 (m=1) to 1.94 eV for (PEA)2(MA)2Pb3I10 (m=3). Owning to the smaller bandgap, favorable vertical growth characteristics, and appropriate energy band structure of (PEA)2(MA)2Pb3I10, planer perovskite solar cells based on (PEA)2(MA)2Pb3I10 exhibit best cell performance. Incorporation of TiO2 nanorod arrays into (PEA)2(MA)2Pb3I7 based perovskite solar cells are further found to be useful in improving the cell performance, ascribing to the improved quality and coverage of the perovskite films, as well as the enhanced electronic contact between the perovskites and the electron transporting layer. By optimizing the TiO2 NR lengths, an efficiency of 3.72% is obtained for (PEA)2(MA)2Pb3I10 perovskite cells with 600 nm-long TiO2NRs as scaffolds, which is more than a time higher than that of the planer analogue device. Our study to design 2D perovskite solar cells demonstrates the importance of material structure and device configuration for efficient solar cells, highlighting the validity of TiO2 nanorods in functionalizing 2D perovskites for photovoltaic applications.