A fluorine-induced high-performance narrow bandgap polymer based on thiadiazolo[3,4-c]pyridine for photovoltaic applications

Abstract

†Electronic Supplementary Information (ESI) available: [TGA plots, temperaturedependent absorption spectra of PDTPT-2TF, HOMO and LUMO distributions, hole mobility measurements, photovoltaic performance of PDTPT-2T with additive, TEM images, 1 H NMR and 13 C NMR spectra]. See Thiadiazolo[3,pyridine (PT) has great potential in constructing high-performance narrow bandgap (NBG) photovoltaic polymers. But to date the best power conversion efficiencies (PCEs) for PT-containing polymers are only around 6%. Herein we report two PT-containing NBG polymers PDTPT-2T and PDTPT-2TF based on 2,2'-bithiophene (2T) and 3,3'-difluoro-2,2'-bithiophene (2TF), respectively. The effects of fluorine substituent on optoelectronic properties are thoroughly investigated. The film absorption onset of PDTPT-2TF is 855 nm, bathochromic-shifted by 24 nm in comparison with that (831 nm) of PDTPT-2T. The lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO) energy levels of PDTPT-2TF are down-shifted by 0.15 and 0.11 eV relative to those of PDTPT-2T, respectively. X-ray diffraction (XRD) patterns indicate that more ordered structure is formed in the solid film of PDTPT-2TF. Furthermore, the miscibility between polymer and [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) is significantly improved through the introduction of fluorine. Consequently, PDTPT-2TF exhibits a high PCE of 8.01% while PDTPT-2T only shows a maximum PCE of 2.65%. The efficiency of 8.01% is the highest one for PT-containing polymers, and more importantly, it is achieved without any processing additives or post-treatments. This work indicates that PT would have great potential as building block to construct high-performance photovoltaic polymers.

The Curious Case of Fluorination of Conjugated Polymers for Solar Cells

“…40 The enhanced planarity, together with various nonbonding interactions introduced by the fluorine atoms, significantly increases the aggregation of the polymers, which improves the absorption properties in some cases. 41 The enhanced planarity can also help improve the π−π interactions and allow the formation of charge transport pathways in the BHJ devices, which can improve the hole mobility, J sc , and FF of such devices. For example, Wang et al 41 found that the hole mobility was improved by nearly 9-fold for PDTPT-2TF with fluorinated bithiophene compared with the nonfluorinated PDTPT-2T (Chart 2).…”

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

“…Thus, we can conclude that the compatibility of PBDTNS-FTAZ:ITIC is much better than that of PBDTBPS-FTAZ:ITIC, resulting in a much better morphology. A favorable morphology is vital for high-performance PSC, which could explain the higher J sc and FF obtained in PBDTNS-FTAZ:ITIC device [ 64 ].…”

Novel Two-Dimensional Conjugated Polymer Containing Fluorinated Bithiophene as Donor and Benzoselenodiazole as Acceptor Units with Vinyl-Terthiophene Pendants for Polymer Photovoltaic Cells

“…Compound 7 was brominated by using N -bromosuccimide to afford Compound 8 . Terthiphene aldehyde intermediate 11 was synthesized by reacting 2,5-dibromothiophene-3-carbaldehyde 10 [ 32 ] with 2.5 equivalents of tributy(4-(2-octyldodecyl)thiophene-2-yl)stannane 9 [ 31 ] using Pd(PPh 3 ) 4 as catalyst under Stille coupling microwave conditions to produce corresponding aldehyde intermediate 11 . The new monomer M1 was synthesized via the Wittig–Horner reaction through the coupling of phosphonic acid diisopropyl ester 8 and aldehyde 11.…”

“…PC 70 BM (> 99%) was purchased from Nano-C (Westwood, MA, USA) and used as received. 5,5′-Bis-(trimethylstannyl)-3,3′-difluoro-2,2′-bithiophene monomer M2 was purchased and used; 4,7-dibromo-5-methylbenzo[ c ][1,2,5]thiadiazole 1 [ 29 ], 5-tributylstannyl-2-thiophene 6 [ 30 ], tributy(4-(2-octyldodecyl)thiophene-2-yl)stannane 9 [ 31 ], 2,5-dibromothiophene-3-carbaldehyde 10 [ 32 ] were prepared according to the literature procedures.…”