Comparing Benzodithiophene Unit with Alkylthionaphthyl and Alkylthiobiphenyl Side-Chains in Constructing High-Performance Nonfullerene Solar Cells

Abstract

Using single-bonded and fused aromatic rings are two methods for extending the π-conjugation in the vertical direction of benzo [1,2-b:4,5-b′] dithiophene (BDT) unit. To investigate which method is more efficient in nonfullerene systems, two novel polymers based on alkylthionaphthyl and alkylthiobiphenyl substituted BDT named PBDTNS-FTAZ and PBDTBPS-FTAZ are designed and synthesized. Two polymers only exhibit small differences in structure, but huge differences in photovoltaic properties. They are studied by blended with 3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)indanone)-5,5,11,11-tetrakis(4-hexylphenyl)dithieno [2,3-d’:2,3’-d’]-s-indaceno [1,2-b:5,6-b’] dithiophene (ITIC). The device based on PBDTNS-FTAZ:ITIC showed the best power conversion efficiency (PCE) of 9.63% with the Voc of 0.87 V, a Jsc of 18.06 mA/cm2 and a fill factor of 61.21%, while the PBDTBPS-FTAZ:ITIC only exhibit a maximum PCE of 7.79% with a Voc of 0.86 V, a Jsc of 16.24 mA/cm2 and a relatively low fill factor of 55.92%. Therefore, extending π-conjugation with alkylthionaphthyl is more effective against constructing nonfullerene solar cells.

Synthesis of a Low-Cost Thiophene-Indoloquinoxaline Polymer Donor and Its Application to Polymer Solar Cells

“…PIQ solution exhibited absorption edge at 663 nm, which red-shifted over 188 nm relative to the monomer 3 solution. Introduction of the electron-donating thiophene to conjugated backbone can significantly enhance electronic delocalization along the chain axis via intramolecular charge transfer [40][41][42]. The monomer 3 solution has a strong absorption at 400-470 nm with a maximum absorption coefficient (ε) of 1.25×10 5 M −1 cm −1 , whereas the polymer PIQ solution has a much larger range of absorption, showing strong absorption in the 400-660 nm range with a slightly higher maximum absorption coefficient of 1.37 × 10 5 M −1 cm −1 (Figure 2b).…”

Tailoring intra-molecular coupling in BDT-based copolymers to enhance their performance in fullerene-free organic solar cells

“…However, the electron donating nature of BDT is lowered by the sulfur atom in its backbone. Substitutions such as alkylthiothenyl, alkylphenyl 17 methylthio 18 and thiophene (Th) of BDT have shown improved electron donating properties hence resulting in a better PCE in OSCs. 19,20 In addition to the electron donating and accepting units, the p-spacer also plays a considerable role in modifying the backbone structure by releasing the steric strain consequently improving their molecular conformation.…”