Molecularly Engineered Cyclopenta[2,1- b;3,4- b′]dithiophene-Based Hole-Transporting Materials for High-Performance Perovskite Solar Cells with Efficiency over 19%

Three cyclopenta[2,1-b;3,4-b′]dithiophene (CPDT)-based organic semiconductors LYC-1-LYC-3 consisting of a central dithiolane ring with triarylamine-based side groups were prepared and utilized as hole-transporting materials (HTMs) in perovskite solar cells (PSCs). Physical studies on HTM LYC-1 indicated that it exhibits high efficiency in hole transfer and a strong hole-extraction tendency from the perovskite layer. The PSC device made with LYC-1 as HTM showed a remarkable performance of 19.07%, which is much higher than the device based on spiro-OMeTAD (17.90%) under a similar condition. Moreover, the hydrophobic nature of LYC-1 protects the perovskite layer effectively from moisture and, therefore, leads to its long-term stability, i.e., retains 85% of initial efficiency after operating over 1000 h. This work demonstrates that the incorporation of a dithiolane ring in the central CPDT core is an effective way of enhancing both efficiency and stability of PSC devices.