New Benzo[1,2-d:4,5-d′]bis([1,2,3]thiadiazole) (iso-BBT)-Based Polymers for Application in Transistors and Solar Cells

Abstract

In this paper we report the rationale and implementation of a new building block for organic electronics based on 4,8-di­(2-thienyl)-benzo­[1,2-d:4,5-d′]­bis­([1,2,3]­thiadiazole) (iso-BBT-T2) and realization of two alkyl-functionalized iso-BBT-tetrathiophene (T4) alternating copolymers (P1 with alkyl = 2DT and P2 with alkyl = 2DH). Compared to the previously investigated small molecules/polymers based on the conventional 4,8-di­(2-thienyl)-benzo­[l,2-c:4,5-c′]­bis­[ l,2,5]­thiadiazole (BBT-T2), the use of the iso-BBT heterocycle widens the polymer band gap to a region (∼1.4 eV) compatible for use in single junction solar cells. The influence of iso-BBT vs BBT structural variation on the molecular structure, electronic characteristics, and optical properties was accessed by DFT computations, single-crystal determination, optical absorption, and electrochemical measurements. In-plane charge transport for P1 and P2 was investigated in an organic thin-film transistor (OTFT) structure demonstrating hole mobilities approaching 1 cm2 V–1 s–1 and further enhanced by off-center spin-coating method to 1.32 cm2 V–1 s–1. Using PC61BM as acceptor, a remarkable PCE of 10.28% was achieved for P1 along with a current density > 20 mA/cm2. The substantial PCEs of these devices, despite the relatively narrow donor energy gap, is due to retention of high open circuit voltages ( V oc > 0.8 V) as the result of the small energy loss (E loss < 0.6 eV). Atomic force microscopy, transmission electron microscopy, and X-ray diffraction characterization further support the solar cell trends and rationalize structure–property correlations. These results demonstrate that iso-BBT-T2-based polymers are promising candidates for both organic electronics and photonic applications.

Structural Engineering in Polymer Semiconductors with Aromatic N-Heterocycles

“…(d) Structures and single crystals of BBT- and isoBBT-based building blocks. Reproduced from ref . Copyright 2019 American Chemical Society.…”

“…The classic electron-withdrawing unit, BBT, has a low-gap, highly polarized electronic structure, which is beneficial to n -type or ambipolar semiconductors. , The electronic characteristic of iso-BBT shows a much wider gap, which contrasts with that of BBT. Bianchi and co-workers studied the iso-BBT-based polymer semiconductors for use in transistors and solar cells . Iso-BBT was accessed by a ring-closure reaction of p -phenylenediaminethiosulfonic acid with nitrous acid.…”

Two‐Dimensional Conjugated Benzo[1,2‐b:4,5‐b′]diselenophene‐Based Copolymer Donor Enables Large Open‐Circuit Voltage and High Efficiency in Selenophene‐based Organic Solar Cells

“…Solution‐processed organic solar cells (OSCs) have received more and more attention, owing to the advantages of flexible, light‐weight, and large‐area printing by roll‐to‐roll processes [1–14] . In recent years, there have been great developments in efficient OSCs by synthesis of novel electron‐donor and electron‐acceptor materials and innovations in device engineering [15–27] . Apart from the synthesis of nonfullerene acceptors, p‐type conjugated polymeric donors are also very important for further improvement of OSCs [28–32] .…”

High-Performance Polymer Solar Cells with Minimal Energy Loss Enabled by a Main-Chain-Twisted Nonfullerene Acceptor

“…22 Regarding the PSCs based on fullerene derivative acceptor, a low E loss of 0.59 eV with a high PCE reaching 10.28% was reported very recently. 24 Although much progress has been achieved in reducing the E loss for PSCs, there is still much room for minimizing their E loss . Figure S1 expanding the absorption profile and enhancing the efficient charge transportation.…”

“…In the case for the PffBT2T-TT:O-IDTBR-based device, a promising PCE of 10.4% can be realized, with a notable V oc of 1.08 V and a low E loss of 0.55 eV, in spite of very small both Δ E HOMO and lowest unoccupied molecular orbital (LUMO) offset (Δ E LUMO ) (Δ E HOMO = 0.09 eV and Δ E LUMO = 0.03 eV) . Regarding the PSCs based on fullerene derivative acceptor, a low E loss of 0.59 eV with a high PCE reaching 10.28% was reported very recently . Although much progress has been achieved in reducing the E loss for PSCs, there is still much room for minimizing their E loss .…”