Several carbazole derivatives (V866, V867 and V868) as hole transporting materials (HTMs) in perovskite solar cells are designed to explore the functional group position effect on electrochemical properties. The material properties are studied on the first-principle calculations combined with the Marcus theory. The results illustrate that V866 (ortho-position) has the suitable HOMO energy level matched with the metal electrode (-5.1 eV) and the perovskite absorption layer (-5.4 eV). Moreover, the molecular planarity of HTMs with the ortho-position functional groups is improved, which enhances intermolecular face-to-face $π-π$ stacking degree. Compared to V867 and V868, the largest hole mobility value (0.007 ${\rm cm}^2 {\rm V}^{-1} {\rm s}^{-1})$ of V866 is obtained due to its modified molecular planarity. Therefore, V866 (ortho-position) is indeed an excellent carbazole HTM. Our theoretical investigation of HTMs is helpful for understanding the hole transporting behaviors and developing higher performance HTMs.

In the present paper, the non-radiative transition ${\rm S}_1→{\rm S}_0$ of pyrazine was investigated by employing the improved Born-Oppenheimer adiabatic approximation, in which the conical intersection is shown to be avoided. Vibrational frequencies, normal coordinates, and non-adiabatic coupling matrix elements were obtained by ab initio quantum chemical methods. Calculated rate constants of internal conversion ${\rm S}_1→{\rm S}_0$ are $τ(υ=0)=61.7 $ ps and $τ(υ=1)=61.2$ ps in good agreement with the experimental findings.

The polymer with D-A structure has been certified a significant role as donor materials of organic solar cells (OSCs) for its outstanding light absorption. In this work, the properties of pyridine based and fused cyclic based D-A polymer was studied by means of DFT and TD-DFT theory under PBE0/6-31G(d) level. Based on the reported polymer D1, pyridine and fused cyclic were introduced to D2, D3 and D4. Compared with polymer lacking the pyridine and fused cyclic, the pyridine and fused cyclic based exhibits better planarity, lower HOMO energy and broader absorption properties, which are helpful to get a higher $V_{oc}$ and $J_{sc}$. Moreover, fused cyclic based as well as pyridine monocycle and pyridine fused cyclic based polymer shows the ability to enhance the hole transfer rate. Hence, the approach of introducing pyridine and fused cyclics to polymer donor is a feasible way to modulate the electron-withdrawing capability in D-A polymer chain thereby promotes the performance of the OPV devices.