# Low Band Gap Fused Bicyclic Polymers with Heteroatoms Se and Te: A DFT-PBC Study

## TL;DR

This paper uses computational methods to study the electronic properties of polymers with selenium and tellurium atoms, aiming to design materials with low band gaps for organic electronics.

## Contribution

The study introduces new fused bicyclic polymers with Se and Te heteroatoms and evaluates their low band gaps using DFT-PBC simulations.

## Key findings

- A planar polymer structure with Se atoms at 4–6 connection positions has a band gap of 0.779 eV, close to the experimental value of 0.76 eV.
- Polymers with different heteroatom pairs (Se–Te, Te–Se, Te–Te) also show low band gaps ranging from 0.730 to 0.905 eV.
- The conducting properties of the polymers are comparable to benchmark materials like polypyrrole and polythiophene.

## Abstract

Designing low band
gap conjugated polymers is critical for the
development of advanced materials in organic electronics. This study
focuses on DFT-PBC analysis of a series of bicyclic fused polymers
containing heteroatoms Se and Te, using the hybrid functional B3PW91.
The polymer geometries defined by cells containing two monomers connected
in different configurations were initially optimized with an assumption
that all the atoms are on the same plane due to interchain interactions
in the solid state. Subsequently, the structures were optimized without
these restrictions, starting from the nearly planar geometry, as small
deviations were anticipated due to insufficient interchain interactions
required for planar geometry. According to the band structure calculations,
the band gap value for the planar structure with 4–6 connection
positions, where two Se atoms occupy both heteroatom positions, was
found to be 0.779 eV, which is very close to the experimentally determined
value of 0.76 eV (Patra 11). The finding indicates that polymerization
primarily occurs through this connection within theoretical limits.
The band gap values for other structures with the same connection
positions but different heteroatom pairs (Se–Te, Te–Se,
and Te–Te) were also low, at 0.905, 0.745, and 0.730 eV, respectively.
Conducting properties of the title polymers were assessed by comparing
band gaps, bandwidth, and effective mass values. In conclusion, the
planar structures of the polymers with 4–6 and 2–4 connections
exhibit bandwidths comparable to those of polypyrrole and polythiophene,
with their effective masses that are either improved or comparable
with these benchmark materials. Furthermore, atomic and subshell compositions
of the frontier orbitals were analyzed to gain insight into the variation
of the band gap as a function of the heteroatom.