Abstract
In perovskite solar cells (PSCs), the hole extraction/transport and the device stability are strongly dependent on the molecular structure of the hole transporting material (HTM). Designing of organic HTMs that are efficient for charge extraction and transport when integrated into optoelectronic devices is of great importance. The two fabricated devices: TiO2/CH3NH3PbI3/PYOMe/Au and TiO2/CH3NH3PbI3/spiro-OMeTAD/Au PSCs, where the HTMs in the two devices are a pyrene-core N1,N1,N3,N3,N6,N6,N8,N8-octakis(4-methoxyphenyl)pyrene1,3,6,8-tetraamine (PYOMe) and the classical spiro-OMeTAD, respectively, recorded very comparable performance. The overall power conversion efficiencies are 12.4 and 12.7%, respectively. However, the preparation of PYOMe is more cost-effective, and it is predicted that the PY-core compounds will have faster charge-transport ability compared to the spirobifluorene core. Herein, we have engineered a PY-core compound (PYOMe) with groups of different electron-donating abilities at the para-position. DFT/M06/6-311G(d,p) and TDDFT/M06/6-31G(d) levels were used to investigate the geometrical, electronic and optical properties of these derivatives in their neutral, cationic and anionic forms. The frontier orbital energy levels and their spatial distribution were computed for all derivatives and compared in the neutral and ionic forms. The results indicated that groups with different electron-donating abilities in the PY-core framework lead to different optical properties. According to the calculations, stronger electron-donating substituents remarkably destabilize the HOMO and LUMO, while weaker electron-donating substituents stabilize them. The reorganization energy, electron affinity, and ionization potential were also calculated and discussed. Finally, to shed light on the intrinsic mobility, the charge transport properties of three HTMs as representative examples were calculated and analyzed.