The Impact of Benzothiadiazole on the Optoelectronic Performance of Polymer/PC₇₁BM Blend Films and Their Application in NIR Phototransistors

Abstract

D‐A conjugated polymers P1 and P2 are synthesized by copolymerizing bisthiophene‐fused diketopyrrolopyrrole (4,11‐bis(2‐decyltetradecyl)‐7H,14H‐thieno[3',2':7,8]‐indolizino[2,1‐a]thieno[3,2‐g]indolizine‐7,14‐dione, BTI) with terthiophene and thiophene‐benzothiadiazole‐thiophene, respectively. Molecular packing is characterized by X‐ray diffraction. The film morphology is characterized by atomic force and scanning electron microscopy. The vertical phase separation is characterized by XPS. The mechanism of film morphology formation is explained from intermolecular interaction, kinetics, and surface free energy. The spin‐coated films of polymers blended with PC71BM are served as semiconductor layers in near‐infrared (NIR) phototransistors. The impact of morphology on optoelectronic performance is analyzed. The mobility of organic field effect transistors based on P1 or P2 thin films remains constant with the addition of PC71BM with weight ratio being less than 50%. The main reason is that π–π stacking in both P1 and P2 thin films is at all directions and PC71BM does not disturb the charge percolation path. Benzothiadiazole in P2 enables stronger mutual attraction between P2 and PC71BM, and therefore large contact area between P2 and PC71BM forms in the heterojunction. The photoresponsivity improves by 2 times for NIR phototransistors based on P2/PC71BM when decreasing light intensity from 63 to 1.8 µW cm‐2. The above results suggest a feasible conjugated polymer design rule for high sensitivity NIR phototransistors.

Conjugated polymers with near-infrared (NIR) optical absorption: structural design considerations and applications in organic electronics

“…241 P54 incorporates BT with a π-extended fused ring DPP derivative as a second acceptor repeat unit affording strong NIR optical absorption ( λ max / E g = 829 nm/1.27 eV). 242 When blended with PC 71 BM in OPTs, P54 provides an R (850 nm) = 118 A W −1 with improved photoresponsivity at lower light intensities (1.8 μW cm −2 ). This trend in responsivity is attributed to a desirable morphology/microstructure for the P54 /PC 71 BM blends.…”

Vinyl-Flanked Diketopyrrolopyrrole Polymer/MoS2 Hybrid for Donor–Acceptor Semiconductor Photodetection

“…DPP-containing polymers have also been used in photodetectors as active materials. ,, For example, Wang and co-workers reported a high-performance broadband photodetector based on the combination of the electron-deficient DPP and benzothiadiazole (BT) molecules, leading to devices with a specific detectivity value over 10 12 Jones between 320 and 930 nm under −0.1 V bias . On the other hand, two-dimensional (2D) semiconductor transition-metal dichalcogenides (TMDCs) are desirable as photodetectors because their band gaps lie in the visible region of the solar spectrum, and they possess very high photoresponsivity and external quantum efficiencies. − They show tremendous potential for optoelectronic applications due to their tunable band gaps (from indirect in the bulk to direct in a single atomic layer) and stable performance in ambient conditions.…”

Implementing the donor–acceptor approach in electronically conducting copolymersviaelectropolymerization

“…As the standard electrode potentials decrease and more monomer units are joined together, 19,20 electropolymerization of a dimer ( e.g. , bisthiophene, T 2 ) 21 can be carried out at a much lower potential than that of the monomer (thiophene, T). The electropolymerization of the trimer (terthiophene, T 3 ) 22 can be affected at even a lower potential than that required for the dimer.…”