Efficient tuning of triphenylamine-based donor materials for high-efficiency organic solar cells

Small molecular donors (SMDs) manifest promising photovoltaic performance and rapid progress in solar cells community. Herein, we investigate high-performance triphenylamine (TPA) small molecular donors for solar cells applications. We specifically designed four donor molecules (D1-D4) with a strong donor moiety of triphenylamine (TPA) linked to four different end-capped units. The structure-property relationship and effects of end-capped units on D1-D4 are theoretically calculated and compared with reference molecule R. DFT and TDDFT approach have been employed and assessments of photophysical characteristics, frontier molecular orbitals (FMOs), reorganization energies, density of state (DOS) and overlap population density of state (OPDOS), open circuit voltages (V-oc), transition density matrix (TDMs), surfaces and charge transfer analysis were conducted. In comparison to synthesized reference molecule R, designed D1-D4 molecules show significant and comparable optoelectronic properties. The D3 designed molecule is proven as the best candidate for solar cells applications than all other due to its promising photovoltaic properties involving the lowest band gap (3.329 eV) and excitation energy (3.094 eV), small reorganization energies for electron (lambda(e) = 0.110 eV) and hole (lambda(h) = 0.055 eV), low binding energy (E-b = 0.221 eV), highest lambda(max) values 396.69 nm, 400.63 nm both in gas and solvent form, respectively. This theoretical designed model confirms that the end-capped unit modifications proves an efficient alternative solution in achieving the desired optoelectronic properties. Therefore, D1-D4 designed molecules are outstanding and highly recommended to experimentalists for developments of highly efficient solar cells devices in future.