Electronic density of states and conduction properties of Type-II staggered copolymers of thiophene based donor-acceptor polymers

Abstract

Using the <i>ab initio </i>band structure results of three thiophene based donor-acceptor polymers, PHTH (A)_x, PFTH (B)_x and PCNTH (C)_x, the electronic density of states of their various periodic and aperiodic copolymers (A_m B_n)_x, (A_mC_n)_x and (B_mC_n), belonging to the class of Type-II staggered have been determined in tight binding approximation. The unit cell of

these donor acceptor polymers consists of bicyclopentadithiophene unit bridged by an electron accepting group >C=CH₂ in PHTH (A)_x, >C=CF₂ in PFTH (B)_x and >C=C(CN)₂ in PCNTH (C)_x. The trends obtained in the electronic structures and conduction properties of these copolymers as a function of block size, composition and the arrangement of blocks in the copolymer chains are discussed. The results are important guidelines for designing novel polymers with desired conduction properties.