Synthesis of linear unsubstituted poly(4,4′‐triphenylamine) via Suzuki‐Miyaura coupling of an asymmetric AB monomer

Abstract

Polytriarylamines (PTAAs) are amorphous polymers that can be reversibly oxidized to generate stable radical cations. Despite exhibiting a low charge carrier mobility, PTAAs are widely used as hole‐transporting layers in perovskite solar cells due to their excellent stability under ambient conditions. The highest occupied molecular orbital (HOMO) energy levels of PTAA are generally in the range of −5.1 to −5.2 eV, and therefore slightly too high for an optimal alignment with perovskites. Most linear PTAAs carry two or three methyl substituents per repeating unit. While these prevent crosslinking of chains and thus provide reaction control, the electron‐donating substituents raise the energy level of the HOMO. Unsubstituted PTAA on the other hand is usually obtained crosslinked via oxidative polymerization, while nickel‐catalyzed Grignard polycondensation leads to inclusion of impurities. We report the synthesis of linear unsubstituted PTAA using Suzuki‐Miyaura coupling of a novel asymmetric monomer, 4‐((4‐bromophenyl)(phenyl)amino)phenyl)boronic acid M1. Based on matrix‐assisted laser desorption/ionization‐time of flight (MALDI‐TOF) and 1H NMR analysis, we can conclude that the hydrogen‐terminated linear polymer is obtained. The determined HOMO energy level of −5.47 eV is a favorable match for many perovskite systems.

Solvent-Activated Transformation of Polymer Configurations for Advancing the Interfacial Reliability of Perovskite Photovoltaics

“…As discussed previously, methyl substituents linked to the branched benzene ring in PTAA as the electron-donating groups could raise the highest occupied molecular orbital (HOMO) level of PTAA compared to unsubstituted poly(4,4′triphenylamine) (PTPA) (Figure S12). 32 To gain more insights into the effect of 2-Me treatment on the surface conformation of PTAA, UPS was applied to evaluate the variation of HOMO levels of PTAA films before and after solvent treatment. 33 As shown in Figure 3c,d, the HOMO levels of pristine, DMF-treated, and 2-Me-treated PTAA films were estimated to be −5.06, −5.08, and −5.11 eV, respectively.…”