Donor–Acceptor Conjugated Polymer Based on Naphtho[1,2-c:5,6-c]bis[1,2,5]thiadiazole for High-Performance Polymer Solar Cells

Abstract

Donor-acceptor conjugated polymers PBDT-DTBT and PBDT-DTNT, based on 2,1,3-benzothiadiazole (BT) and naphtho[1,2-c:5,6-c]bis[1,2,5]thiadiazole (NT), have been designed and synthesized for polymer solar cells. NT contains two fused 1,2,5-thiadiazole rings that lower the band gap, enhance the interchain packing, and improve the charge mobility of the resulting polymer. Consequently, the NT-based polymer PBDT-DTNT exhibited considerably better photovoltaic performance with a power conversion efficiency (PCE) of 6.00% when compared with the BT-based polymer PBDT-DTBT, which gave a PCE of 2.11% under identical device configurations.

Location, Location, Location ‐ Strategic Positioning of 2,1,3‐Benzothiadiazole Units within Trigonal Quaterfluorene‐Truxene Star‐Shaped Structures

“…[ 23 ] BT has, moreover, been combined with other thiophene based units to achieve smaller optical gap solar cell polymers and molecular light absorbers for dye-sensitized solar cells. [24][25][26][27] A greater understanding of the electronic interplay between the BT and neighboring units in a given structure would be highly benefi cial to the organic electronics community -particularly at the most fundamental level in the structural design of new semiconductors. To this end, the series of structural isomers T4BT-A to T4BT-E allows a thorough investigation of the effect of subtle variations in environment on the infl uence of BT addition to a 9,9-dialkylfl uorene chain.…”

“…The lowest energy of these (labelled III in Figure 2 ) involves a LUMO that is spatially localized on the BT unit and it is generally considered to possess a degree of charge-transfer character [ 28 , 30 ] though not as much as the HOMO-LUMO transition in solar cell materials wherein the BT is fl anked by more strongly electron donating thiophene containing moieties. [23][24][25][26] The second (labelled II in Figure 2 ) links the HOMO to higher lying delocalized unoccupied molecular orbitals that are reported either to be centered on 9,9-dialkylfl uorene units [ 11 ] or more fully delocalized, involving the BT unit as well. [ 30 ] This transition is similar in character to the delocalized-delocalized π -π * HOMO-LUMO transition of T4 [ 34 ] and poly(9,9-dialkylfl uorene)s. [ 11 ] We have undertaken further DFT/TD-DFT calculations to gain a clearer insight into the specifi c electronic structure of our T4BT-X compounds.…”

Incremental optimization in donor polymers for bulk heterojunction organic solar cells exhibiting high performance

“…1.58 eV) than PBDT-DTBT due to the electron-deficient NT unit. 7 Interestingly, the HOMO and LUMO energy levels can also be tuned without significantly affecting the band gap. For example, on replacing the hydrogen atoms on the DTBT unit of PBnDT-DTBT with fluorine atoms, the HOMO and LUMO energy levels of PBnDT-DTffBT were both lowered by about 0.14 and 0.20 eV, respectively, while maintaining the band gap at about 2.2 eV.…”

Development of donor–acceptor copolymers based on dioxocycloalkene-annelated thiophenes as acceptor units for organic photovoltaic materials

“…On the other hand, the development of new acceptor units is still vital for synthesizing D-A copolymers because effective acceptor units are limited to 2,1,3-benzothiadiazole, 8 diketopyrrolopyrrole, 10 thieno [3,4-c]pyrole-4, 6-dione, 11 thieno [3,4-b]thiophene with electron-withdrawing substitutents 12 and naphtho[1,2-c:5,6-c']bis [1,2,5]thiadiazole. 13 We have investigated the development of new electron-accepting materials for n-channel organic field-effect transistors (OFETs) and have applied the developed electron-deficient units to D-A copolymers for OPVs.…”