Influence of 4‐fluorophenyl pendants in thieno[3,4‐b]thiophene‐benzo[1,2‐b:4,5‐b′]dithiophene‐based polymers on the performance of photovoltaics

Abstract

Polymers consisting of benzo[1,2‐b:4,5‐b′]dithiophene and thieno[3,4‐b]thiophene units (PTB‐based polymers), either fully or partially containing 4‐fluorophenyl pendants, are synthesized as electron donor materials for inverted‐type polymer solar cells (PSCs). The influence of the 4‐fluorophenyl pendant content on the thermal and optical properties, the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO), the hole mobilities, and photovoltaic performances are investigated. As the 4‐fluorophenyl pendant content increased, the HOMO and LUMO of the polymers were deepened proportionally and the open‐circuit voltages of the PSCs improved. Incorporation of 4‐fluorophenyl pendants into the polymers also affected the crystallinity, orientation, and compatibility with [6,6]‐phenyl‐C61‐butyric acid methyl ester in the active layers, leading to nonlinearities in the short‐circuit current densities, and fill factors. The incorporation of an appropriate number of 4‐fluorophenyl pendants enhanced the power conversion efficiencies of the PSC devices from 2.25 to 3.96% for identical device configurations. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 1586–1593

Synthesis of Thieno[3,4-b]thiophene-Based Donor Molecules with Phenyl Ester Pendants for Organic Solar Cells: Control of Photovoltaic Properties via Single Substituent Replacement

“…Recently, we have developed a series of PTB‐based polymers, which have p ‐substituted phenyl ester pendants in their TT repeating units, and found that their highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels can be efficiently controlled by varying the p ‐substituents on the phenyl rings . Additionally, PTB‐based ternary copolymers consisting of two types of TT components with 4‐fluorophenyl and n ‐octyl esters have also been synthesized, and precise control of the HOMO levels of the resulting polymers has been achieved by changing the feed ratio of two TT comonomers . When these ternary copolymers were used as electron donors in OPV devices, a higher open‐circuit voltage ( V oc ) was attained using the polymer with the deeper HOMO level.…”

Organic Photovoltaics Based on Poly(3,4-phenylenedioxy-2,5-thienylenevinylene)s

“…The lower HOMO energy of PPhDOTFV compared to PPhDOTV originates from the strongly accepting nature of fluorine in the phenylene part of PPhDOTFV, which is beneficial for obtaining a higher V oc in BHJ OPVs. [19][20][21] The energy levels of the lowest unoccupied molecular orbital (LUMO) of PPhDOTV and PPhDOTFV estimated from their E g values and HOMO levels were situated at ¹3.48 and ¹3.68 eV, respectively.…”