Bromine-based hybrid perovskites exhibit excellent performance as the top layer of tandem cells, but their overall efficiency as single-junction devices is still very limited. In this work, trimethylolpropane ethoxylated triacrylate (TET), which can form a cross-linking polymer at the grain boundary after heating at 150 °C, is introduced as an additive in FAPbBr3-based perovskite solar cells. The FAPbBr3 film with TET exhibits pinhole-free crystal grains with a large grain size. With a concentration of 5 mg/mL TET, the average grain size increases from 313 to 505 nm. What is more, Raman spectroscopy and X-ray photoelectron spectroscopy demonstrate that the cross-linked TET has a strong interaction with FAPbBr3, which can passivate the defects of grain boundaries. Therefore, the FAPbBr3-based perovskite solar cells with TET achieve a power conversion efficiency of 8.93%. As we know, this is the highest value in FAPbBr3-based hybrid perovskites with an inverted planar structure. This work provides a new insight into the in situ cross-linking additive TET, which only exists at the grain boundary, does not enter the lattice, and has a crystallization control and defect passivation effect on FAPbBr3 thin films, which will provide a new direction for further improving the performance of FAPbBr3 perovskite solar cells.

Ending groups play a vital role in regulating the band gap and energy level of low-band gap nonfullerene acceptors (NFAs). In this work, a novel NFA, BTP-IS, is synthesized by adopting sulfonyl-based ending groups. Compared to the ketone counterpart BTP-IC, BTP-IS exhibits a red-shift in absorption spectra with lower lowest unoccupied molecular orbital level. More importantly, the BTP−IS-based organic solar cells with PM6 as donor present a high power conversion efficiency (PCE) of 12.79%, which is much higher than that of the BTP-IC device (PCE of 7.54%). The efficient charge transfer between the polymer donor and NFA acceptor, the balance charge transport, and the fine photoactive morphology bear on the effective exciton dissociation and charge collection in the BTP-IS device, which induces high short circuit current (J SC ) and fill factor (FF) values. This research has shed light on designing novel NFAs from the perspective of ending groups.