Design of Cone-Shaped Hole Transporting Material Organic Structures for Perovskite Solar Cells Applications

This study reports design and synthesis of cone shaped hole transporting materials (HTM, i. e., H1 and H2). They are based on triphenylamine (TPA) and phenothiazine donors attached with two TPA moiety via electron rich π-spacer (phenyl acrylonitrile). π-spacers are proven to enhance the power conversion efficiency (PCE) of perovskite solar cells (PSCs) in the literature. Due to the electron withdrawing nature of the π-spacer and the extended conjugation present in the HTMs proposed, a gradient for charge flow within the molecule is expected. This property is essential to transfer the electron from the HOMO of HTMs to the valence band of the perovskite via the arms of the HTMs. These HTMs do not show strong absorption in the visible region, exhibit high stokes shift and have their HOMO positioned above the perovskite's valence band. HTM layer of the PSCs were fabricated by a solution process method, at ambient conditions. A PCE of ∼1.9% at 1 sun condition was obtained, while under similar conditions the standard HTM (S-OMeTAD) exhibited a PCE of 1.3%.