Dopant-Free Hole Transport Materials Based on a Large Conjugated Electron-Deficient Core for Efficient Perovskite Solar Cells

Hole transport materials (HTMs) play a significant role in device efficiencies and long-term stabilities of perovskite solar cells (PSCs). In this work, two simple dopant-free HTMs are designed with a large conjugated electron-deficient core. On the one hand, a large coplanar backbone endows enhanced pi-pi stacking and reduced hole hopping distance. On the other hand, the incorporation of electron-deficient unit can easily tune the energy levels as well as increase hole mobilities. Combining these two advantages together, 12,13-bis(2-ethylhexyl)-3,9-diundecyl-12,13-dihydro[1,2,5]thiadiazole[3,4-e]thieno[2 '',3 '':4,5]thieno[2 ',3 ':4,5]pyrrolo[3,2-g]thieno[2 ',3 ':4,5]thieno[3,2-b]indole is chosen as the large electron-deficient core to construct two novel dopant-free HTMs, Y6-T and Y-T. Both Y6-T and Y-T behave suitable highest occupied molecular orbital levels, good hole mobilities, as well as strong hydrophobicities. After careful device optimization with a passivation agent, Y-T delivers an impressive power conversion efficiency of 20.29%, which is higher than that of Y6-T (18.82%) and doped spiro-OMeTAD (19.24%). Moreover, PSCs based on Y6-T and Y-T show much better long-term stabilities than spiro-OMeTAD due to the intrinsic hydrophobicity. Therefore, this work provides a promising candidate as well as a useful design strategy for exploring dopant-free HTMs, which may pave the way for the commercialization of PSCs.

Automated summary

Two novel dopant-free HTMs, Y6-T and Y-T, with large conjugated electron-deficient cores are designed in this work, showing enhanced pi-pi stacking, reduced hole hopping distance, and increased hole mobilities. With careful device optimization, Y-T achieves an impressive power conversion efficiency of 20.29% and better long-term stability compared to Y6-T and doped spiro-OMeTAD. This work provides a promising candidate and useful design strategy for exploring dopant-free HTMs in commercializing PSCs.