Theoretical Study On Organic Polymer Photovoltaic Materials

The paper applied the quantum chemistry methods and systematically studied the following three systems: (1) containing benzo[1,2-b:4,5-b']dithiophene conjugated polymer; (2) poly(3-(phenylenevinyl)thiophene) with conjugated side chains conjugated polymers and derivatives; (3) indolocarbazole-acceptor conjugated copolymers.Firstly, poly(4,8-bis(dodecyloxy)benzo[1,2-b:4,5-b']dithiophene)(PBDT), poly(4,8-bis (dodecyloxy)benzo[1,2-b:4,5-b']dithiophene)-alt-(2,5-thiophene)(PBDTT), poly(4,8-bis (dodecyloxy) benzo[1,2-b:4,5-b']dithiophene)-alt-(2,9-thieno[3,4-b]pyrazine)(PBDTTPZ) were geometrically optimized by the density functional theory (DFT) and the Becke–Lee–Young–Parr composite exchange correlation functional (B3LYP). Based on the optimized geometries, the optical properties are calculated by employing time dependent density functional theory(TD-DFT), to obtain the lowest excitation energy (Eg) and the absorption wavelength including electron correlation. The HOMO-LUMO gap (△H-L) is equal to the energy difference between the LUMO and the HOMO (△H-L=ELUMO-EHOMO). The calculated results in polymer are in good agreement with experiment results, and the results provide some useful references to control band gap and absorption band of conjugated polymers.Secondly, the structural and electronic properties of these three poly[3- (phenylenevinyl)thiophene] (P3PVT)s (PEHPVT)n, (PT1)n and (PT4)n were calculated by DFT and TD-DFT respectively.△H-L and Eg values of each polymer are obtained by extrapolating those of the oligomers to the inverse chain length equal to zero (1/n =0). The results of this work show that polymers with conjugated side-chain can modulate the absorptions and HOMO-LUMO band gaps, indicating that the calculations are capable of accurately describing the optical and electronic features of the investigated polymers, with a quantitative agreement with the experimental data.At last, poly[2,8-(5,11-di(2-ethyl-hexyl)indolo[3,2-b]carbazole)-alt-5,7-(2,3-dido- de-cylthieno[3,4-b]pyrazine)] (P28IC-TP12), poly[2,8-(5,11-di(2-ethylhexyl)indolo [3,2-b]carbazole)-alt-4,7-(2,1,3-benzothiadiazole)] (P28IC-BT), poly[2,8-(5,11-di(2- ethylhexyl)indolo[3,2-b]carbazole)-alt-5,7-(2,3-bis(4-(2-ethylhexyloxy)phenyl)-thieno[3,4-b]pyrazine)] (P28IC-TPO) were geometrically optimized. Based on the optimized geometries, the optical properties are calculated by employing TD-DFT. The electronic properties of the neutral molecules, HOMO–LUMO gaps (ΔH-L), in addition to IP and Ea, are studied using B3LYP density functional theory.