Cyclooctatetrathiophene-Cored Three-Dimensional Hole Transport Material Enabling Over 19% Efficiency of Perovskite Solar Cells

In this work, a rigid three-dimensional cyclooctatetrathiophene was the core component in the construction two hole transporting materials (HTMs), COTT-1 and COTT-2. Their photophysical, electrochemical, and thermal properties were systematically investigated in a combination of experimental and simulation methods. COTT-1-and COTT-2-based perovskite solar cells (PSCs) were tested, exhibiting power conversion efficiency (PCE) of 8.4% and 17.7%, respectively, which are similar to that of a Spiro-OMeTAD-based device (18.2%) under the same conditions. PCE was further increased to 19.2% using COTT-1 as an interfacial layer and COTT-2 as the HTM. These phenomena were analyzed by means of photoluminescence (PL), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and atomic force microscopy(AFM) experiments, which demonstrated the potential of the cyclooctatetrathiophene-cored hole transport material.