Dopant-free star-shaped hole-transport materials for efficient and stable perovskite solar cells

Two star-shaped TPA-based small-molecule materials (Z1012 and Z1013) were designed and synthesized in this paper. These molecules show high hole mobility and suitable energy levels for CH3NH3PbI3-based perovskite solar cells. Photovoltaic cells based on the Z1013 without any dopants or additives achieve an excellent power conversion efficiency (PCE) of 15.4%, which is comparable to devices based on state-of art p-doped spiro-OMeTAD. Moreover, the devices based on these two HTM5 show much better stability than that of devices based on spiro-OMeTAD when aging in ambient air both at room temperature and 80 degrees C. These results demonstrate that star-shape TPA5 could be excellent dopant-free HTM5 for perovskite solar cells and hold promise to replace the p-doped spiro-OMeTAD, which is important for the fabrication of cost-effective and stable devices. (C) 2016 Published by Elsevier Ltd.