First-principles study to explore the long-range exciton dissociation and reduced binding energy in...

We designed six new electron transport materials: M1-M4 and their extended derivatives, M5 and M6, based on a 5,10-dihydrothieno[3',2':4,5]pyrrolo[2,3-f]thieno[2,3-b]indole core. These D-A-type electron transport layers (ETLs) are intended for use in perovskite solar cells (PSCs). Using DFT and TD-DFT methods in gas, toluene, and ethanol phases, we systematically evaluated the substituent contribution to molecular planarity, frontier molecular orbitals (FMOs), absorption spectra, hole-electron reorganization energy, density of states, light-harvesting efficiency (LHE), exciton binding energy (E _b), and transition density matrix (TDM). Compared to the reference (3.72 eV), the developed ETMs have much smaller band gaps (1.35-1.62 eV), with M6 having the smallest gap (1.35 eV). With deviations of 0.17 to 0.23 eV, the LUMO levels (-4.07 to -4.13 eV) are in good alignment with the perovskite conduction band (-3.90 eV for FAPbI₃). E _b drastically drops from 0.36 eV (REF) to 0.33-0.20 eV for M1-M6, with M6 exhibiting the lowest E _b value (0.20 eV). All ETMs exhibit outstanding LHE (0.83-0.95), with M5 reaching 0.95. As coulomb energies (E _coul) drop from 5.57 eV (M1) to 1.17 eV (M6), charge transfer distances (D) gradually increase from 0.77 Å (M1) to 16.02 Å (M6), demonstrating an inverse correlation (R ² = 0.98). The theoretical V _OC has fill factors of 88.4-89.0% and varies from 1.025 V (M2) to 1.091 V (M6). With an anticipated PCE of 21.5%, the triphenylamine group (M6) offers the greatest V _OC (1.091 V), longest D (16.02 Å), lowest E _b (0.20 eV), and lowest E _coul (1.17 eV). With an anticipated PCE of 20.5%, M5 displays λ _max = 764 nm, LHE = 0.95, and λ _e = 0.36 eV. Excellent planarity (MPP = 0.350-0.445 Å) and balanced properties (expected PCE: 19.8%) are displayed by indole-based M2-M4. As donor tuning maximizes absorption and V _OC, the acceptor-dominated LUMO ensures electron transport. Additionally, the synthetic accessibility score demonstrated the practical viability of the developed chromophores.