Photoluminescence and DFT simulation of conductivity of the p-type doped and charge-injected cis-polyacetylene of Cis-Polyacetylene Semiconductor Material

Photoluminescence (PL) is one of the key observables in experimental characterizations of optoelectronic materials, including conjugated polymers (CPs). Due to their tunable electronic and optical properties, semiconducting CPs have shown great potential in organic solar cells and organic field-effect transistors (OFETs). A simplified model of cis-PA oligomer is used to explain the mechanism of PL of the CPs. We explore the phonon-induced relaxation of the excited states. Here, the dissipative Redfield equation was used with the nonadiabatic couplings as parameters. The relaxation rate of the electron is found to be faster than the relaxation rate of the hole. The dissipative excited-state dynamics were combined with radiative recombination channels to predict the PL spectrum. The simulation revealed similarities in the absorption and emission spectra. The main result is that the computed PL spectrum demonstrates two mechanisms of light emission originating from (i) the inter-band transitions, corresponding to the same range of transition energies as the absorption spectrum, and (ii) intra-band transitions not available in the absorption spectra. [1] The results can be used for improving organic semiconductor materials for photovoltaic and LED applications. Results on single oligomer serve as a basis for the computational predictions of electronic and optical properties of ensembles of cis-PA multiple oligomers in two different forms (a) undoped cis-PA and (b) cis-PA doped by phosphorous fluoride via DFT with hybrid functionals. The comparison of undoped cis-PA under the constraint of injected charge carrier and cis-PA doped by phosphorous fluoride shows that either doping or injection provides very similar features in electronic structure, optical properties, and conductivity. [2] These observations provide a better understanding and practical use of the properties of polyacetylene films for flexible electronic applications.