A star-shaped cyclopentadithiophene-based dopant-free hole-transport material for high-performance perovskite solar cells

An efficient asymmetric structured hole transport material for perovskite solar cells

Hole transport materials (HTMs) play a crucial role in achieving efficient perovskite solar cells (PSCs). In this work, an HTM MF-ACD with an asymmetric structure is designed by introducing two different peripheral end groups. The asymmetric feature increases the molecular dipole of MF-ACD, and endows MF-ACD with good stability and film formation properties, higher hole mobility and conductivity. Consequently, the MF-ACD-based PSC shows a high efficiency of 23.1%, which is much higher than that of the symmetric counterpart. The results show that the asymmetric configuration might be a potential choice to develop more efficient HTMs.

Nexuses Between the Chemical Design and Performance of Small Molecule Dopant-Free Hole Transporting Materials in Perovskite Solar Cells

Perovskite solar cells (PSCs) have grabbed much attention of researchers owing to their quick rise in power conversion efficiency (PCE). However, long-term stability remains a hurdle in commercialization, partly due to the inclusion of necessary hygroscopic dopants in hole transporting materials, enhancing the complexity and total cost. Generally, the efforts in designing dopant-free hole transporting materials (HTMs) are devoted toward small molecule and polymeric HTMs, where small molecule based HTMs (SM-HTMs) are dominant due to their reproducibility, facile synthesis, and low cost. Still, the state-of-art dopant-free SM-HTM has not been achieved yet, mainly because of the knowledge gap between device engineering and molecular designs. From a molecular engineering perspective, this article reviews dopant-free SM-HTMs for PSCs, outlining analyses of chemical structures with promising properties toward achieving effective, low-cost, and scalable materials for devices with higher stability. Finally, an outlook of dopant-free SM-HTMs toward commercial application and insight into the development of long-term stability PSCs devices is provided.