Impact of diethylene glycol chains on indolo [3,2-b]indole based small molecule as dopant-free hole transporting materials for efficient and stable inverted perovskite solar cells

We address a high crystallized small-molecule dopant-free hole transporting material (HTM) based on the indolo [3,2-b]indole (IDID) core unit integrated with flexible diethylene glycol (DEG) side chains, namely DEG-IDIDF. The structural observations by the single-crystal and grazing incidence wide-angle X-ray scattering analyses implied that the DEG side chains provided tight molecular packing and high film crystallinity features, thus enhancing hole mobility. The inverted DEG-IDIDF based PSCs yielded much higher power conversion efficiency of 16.60%, when compared to the commonly used PEDOT:PSS based PSCs (12.04%) under the same inverted PSC structures. Moreover, the DEG-IDIDF based PSCs identified outstanding thermal stability with over 80% of initial efficiency under thermal stress at 60 degrees C for 500 h. Therefore, we anticipate that the ability to control the HTM layer in an inverted p-i-n architecture can spur progress toward the realization of better performance and stable PSCs.

Automated summary

We propose a high crystallized small-molecule dopant-free hole transporting material (HTM) called DEG-IDIDF, based on the indolo [3,2-b]indole (IDID) core unit integrated with flexible diethylene glycol (DEG) side chains. The DEG side chains contribute to tight molecular packing and high film crystallinity, enhancing hole mobility. The DEG-IDIDF based PSCs have higher power conversion efficiency (16.60%) compared to the commonly used PEDOT:PSS based PSCs (12.04%) under the same inverted PSC structures. Moreover, the DEG-IDIDF based PSCs exhibit outstanding thermal stability with over 80% initial efficiency after 500 hours of thermal stress at 60 degrees C.