Peripheral group engineering on hole-transporting materials in perovskite solar cells: Theoretical design and experimental research

Modulation on peripheral groups of hole-transporting materials (HTMs) is a feasible way to control the properties of the energy levels, optical absorption, solubility and hole mobility, to enhance the efficiency of perovskite solar cells (PSCs). In this work, two carbazole core-based HTMs (CQ7 and CQ8) with different peripheral groups are designed. In comparison of Spiro-OMeTAD and CQ8, simulated results show that CQ7 can act as potential HTMs for PSC devices due to its suitable energy levels, good solubility and better hole-transporting ability. To verify the reliability of the simulated results, the molecules CQ7 and CQ8 are synthesized and used to fabricate the PSCs. The experimental results indicates that the PSC device based on CQ7 as HTM yield a 19.60% of power conversion efficiency (PCE), which is higher than that of Spiro-OMeTAD (18.19%) and CQ8 (15.58%) under the same conditions. This is mainly reflected in the improved fill factor and short-circuit current, which is attributed to better hole transport in the CQ7 film and faster hole extraction at the perovskite/CQ7 interface. Conclusively, the experimental data confirm the reliability of the simulation results while providing the feasibility of molecular design strategies to obtain the potential HTMs by adjusting the peripheral groups.