In this work, we introduce a bicomponent hole-transport layer, composed of inorganic NiOx and a donor-acceptor-donor (D-A-D)-structured organic small molecule, for p-i-n planar perovskite photovoltaic (PV) cells. The newly designed D-A-D organic hole-transporting material (HTM), (4',4‴-(1,3,4-oxadiazole-2,5-diyl)bis(N,N-bis(4-methoxyphenyl)-[1,1'-biphenyl]-4-amine)), is shown to be an efficient HTM without a dopant, and methoxy functional units, further introduced to the molecules, are confirmed to be beneficial to passivate the defects in the perovskite, which improves the crystallinity of perovskite and suppresses the nonradiative recombination in the devices, consequently enhancing the performances of PV cells (over 20% efficiency from p-i-n architecture). Furthermore, the decreased defect sites along with the UV-blocking property of the HTM in p-i-n architecture are advantageous in improving the stability of the PV devices.
Keywords: bicomponent; defect-passivation; hole-transport layer; perovskite; solar cell.