Dopant-Free Two-Dimensional Hole Transport Small Molecules Enable Efficient Perovskite Solar Cells

摘要

Developing dopant-free hole transport materials (HTMs) to replace Spiro-OMeTAD is a challenging but urgent issue for commercialization of stateof-the-art n-i-p structured perovskite solar cells (PSCs). Here, this workproposes an effective two-dimensional conjugate engineering strategy to tunemolecular stacking orientation and improve the hole mobility of dopant-freesmall molecule HTMs. For the first time, triphenylamine (TPA) groups areincorporated as side chains of benzo [1,2-b:4,5-b′]dithiophene (BDT) unit toextend the longitudinal conjugate, achieving two donor-acceptor-acceptortype 2D small molecules, namely XF2 and XF3, which show a dominantface-on orientation and better hole transport mobility than the linear smallmolecule XF1. The incorporation of alkoxy Lewis base groups makes XF3 amore effective defect passivator for perovskite surfaces. As a result, the PSCsusing pristine XF3 HTM show a dramatically improved efficiency of 20.59%along with improved long-term stability compared to that of XF1 HTM (powerconversion efficiency (PCE) = 18.84%). A champion efficiency of 21.44% isachieved through device engineering for dopant-free XF3-based PSCs. Theresults show that the building block with longitudinal conjugate extension insmall molecules plays an essential role in the face-on orientation morphologyand elucidates a key design rule for the dopant-free small molecule HTMs forhigh-performance PSCs.