A dopant-free spirobi[cyclopenta[2,1-b:3,4-b ']dithiophene] based hole-transport material for efficient perovskite solar cells

We present the design and synthesis of a promising hole transporting material (HTM) using the 4,40-spirobi[cyclopenta[2,1-b: 3,4-b']dithiophene] derivative (spiro-CPDT) as the core and triarylamines as terminal units. The implementation of the new HTM in CH3NH3PbI3-based perovskite solar cells exhibited an excellent overall power conversion efficiency (PCE) of 13.4% without the use of any dopants and additives which is comparable to 15.0% obtained using p-doped spiro-MeOTAD-based devices. Furthermore, the device based on the new HTM generated a slightly higher open circuit voltage (V-OC) of 971 mV compared to a spiro-MeOTAD (V-OC = 951 mV) based device. The present results demonstrate that spiro-CPDT could be an excellent building block to prepare dopant-free HTMs for perovskite solar cells and holds promise to replace the p-doped spiro-OMeTAD, which is important for the fabrication of cost-effective devices in the future.