Molecular Engineering of Thienyl Functionalized Ullazines as Hole‐Transporting Materials for Perovskite Solar Cells

Abstract

Organic hole‐transporting materials (HTMs) based on the Ullazine core yield so far only moderate power conversion efficiencies of up to 13.08% in perovskite solar cells (PSCs). Aiming to fabricate efficient and stable PSCs, novel Ullazine derivatives bearing thiophene units were designed and synthesized, allowing modulation of the electronic states of the HTMs and further providing defect passivation of the perovskite surface. Experimental and theoretical analysis show that thiophene units with ‐N(p‐MeOC6H4)2 groups improve the conductivity of Ullazine HTMs, boosting the efficiency of PSCs to 20.21%. This value is the highest reported to date for Ullazine‐based HTMs, and is close to the performance of Spiro‐OMeTAD. In addition, unencapsulated PSCs based on the champion Ullazine exhibit superior stability with respect to Spiro‐OMeTAD, retaining nearly 90% of the initial efficiency following 1000 h aging, which is ascribed to a combination of higher water repellency and passivation of defects on the perovskite surface. This work demonstrates the high potential of HTMs based on Ullazine core as substitutes to Spiro‐OMeTAD.

Asymmetrically Substituted 10H,10′H‐9,9′‐Spirobi[acridine] Derivatives as Hole‐Transporting Materials for Perovskite Solar Cells

“…Differential pulse voltammetry (DPV) was used to study the influence of diarylamine group modification on the HOMO level of the materials, see Figure S15. The results show that for both BSA50 and BSA51 , the HOMO levels are higher than the valence band (VB) of the perovskite, FAMAPbI 3 (5.6 eV) [26] . Notably, the HOMO energy is lowered (from −5.30 to −5.37 eV) when the diarylamine group is replaced by the planar analogue, which is consistent with the density functional theory (DFT) calculations.…”

“…The results show that for both BSA50 and BSA51, the HOMO levels are higher than the valence band (VB) of the perovskite, FAMAPbI 3 (5.6 eV). [26] Notably, the HOMO energy is lowered (from À 5.30 to À 5.37 eV) when the diarylamine group is replaced by the planar analogue, which is consistent with the density functional theory (DFT) calculations. The solid-film energy levels of BSA50 and BSA51 on the perovskite films were determined by ultraviolet photoelectron spectroscopy (UPS).…”

“…BSA51 To gain insights into the effect of BSA50 and BSA51 on defect passivation, DFT calculations were performed to study their interactions with a perovskite film with typical Pb-dimer defects. [26,27] To simplify the calculations, the stable (001) surface of MAPbI 3 was introduced for the calculations, and BSA50 and BSA51 models consisting of the corresponding (BSA50) and 3D (BSA51) arylamine moieties, respectively, were considered and their optimized geometries adsorbed on the perovskite (Figure S17). Both were found to interact with Pb-dimers through their O atoms, which may balance extra surface electrons and thus passivate the trap states.…”

“…The greater hydrophobicity of the BSA50 film with its higher water contact angle (76.9°) than the BSA 51 (72.3°, Figure S19) and spiro-OMeTAD film (60.3°) corroborates the improved long-term device stability (Figure 5b and c). [26,28]…”

Asymmetrically Substituted 10H,10′H‐9,9′‐Spirobi[acridine] Derivatives as Hole‐Transporting Materials for Perovskite Solar Cells

“…BSA51 To gain insights into the effect of BSA50 and BSA51 on defect passivation, DFT calculations were performed to study their interactions with a perovskite film with typical Pb-dimer defects. [26,27] To simplify the calculations, the stable (001) surface of MAPbI 3 was introduced for the calculations, and BSA50 and BSA51 models consisting of the corresponding 2D (BSA50) and 3D (BSA51) arylamine moieties, respectively, were considered and their optimized geometries adsorbed on the perovskite (Figure S17). Both were found to interact with Pb-dimers through their O atoms, which may balance extra surface electrons and thus passivate the trap states.…”