Abstract
The ternary polymerization strategy of incorporating different donor and acceptor units forming terpolymers as photovoltaic materials has been proven advantageous in improving power conversion efficiencies (PCEs) of polymer solar cells (PSCs). Herein, a series of low band gap nonconjugated terpolymer acceptors based on two different fused-ring electron-deficient building blocks (IDIC16 and ITIC) with adjustable photoelectric properties were developed. As the third component, ITIC building blocks with a larger π-conjugation structure, shorter solubilizing side chains, and red-shifted absorption spectrum were incorporated into an IDIC16-based nonconjugated copolymer acceptor PF1-TS4, which built up the terpolymers with two conjugated building blocks linked by flexible thioalkyl chain-thiophene segments. With the increasing ITIC content, terpolymers show gradually broadened absorption spectra and slightly down-shifted lowest unoccupied molecular orbital levels. The active layer based on terpolymer PF1-TS4-60 with a 60% ITIC unit presents more balanced hole and electron mobilities, higher photoluminescence quenching efficiency, and improved morphology compared to those based on PF1-TS4. In all-polymer solar cells (all-PSCs), PF1-TS4-60, matched with a wide band gap polymer donor PM6, achieved a similar open-circuit voltage (Voc) of 0.99 V, a dramatically increased short-circuit current density (Jsc) of 15.30 mA cm–2, and fill factor (FF) of 61.4% compared to PF1-TS4 (Voc = 0.99 V, Jsc = 11.21 mA cm–2, and FF = 55.6%). As a result, the PF1-TS4-60-based all-PSCs achieved a PCE of 9.31%, which is ∼50% higher than the PF1-TS4-based ones (6.17%). The results demonstrate a promising approach to develop high-performance nonconjugated terpolymer acceptors for efficient all-PSCs by means of ternary polymerization using two different A–D–A-structured fused-ring electron-deficient building blocks.
Highlights
During the past 5 years, progress in polymer solar cells (PSCs), with their merits of light weight, low cost, semitransparency, and flexibility, has been dominated by the development of polymer donors and A−D−A-structured fused-ring smallmolecule acceptors (SMAs).[1,2]. This rational molecular design of active layer materials and systematic processing and engineering of devices has led to the state-of-the-art power conversion efficiencies (PCEs) exceeding 17% so far.[3−10] Compared to the fused-ring SMA-based systems, all-polymer solar cells composed of polymer donor and polymer acceptor materials have some special advantages, such as excellent morphological stability and mechanical properties, which can cater to the requirements of practical application of flexible devices fabricated by roll-to-roll printing techniques.[11−14] Mainly because of the lack of high-performance polymer acceptors, progress toward efficient all-PSCs has been severely constrained, and their corresponding PCEs still lag behind those of fused-ring SMA-based devices
As shown in Scheme S1, these polymer acceptors were systematically synthesized by Stille-coupling polymerization of three monomers, including two brominated fused-ring SMA building blocks of IDIC16-Br and ITIC-Br with different feeding ratios and a stannylated nonconjugated linkage of bis(trimethylstannyl)-substituted dithiobutyl bithiophenes
We developed a series of low band gap nonconjugated terpolymer acceptors based on two different fused-ring SMA building blocks IDIC16 and ITIC, where ITIC
Summary
During the past 5 years, progress in polymer solar cells (PSCs), with their merits of light weight, low cost, semitransparency, and flexibility, has been dominated by the development of polymer donors and A−D−A-structured fused-ring smallmolecule acceptors (SMAs).[1,2] This rational molecular design of active layer materials and systematic processing and engineering of devices has led to the state-of-the-art power conversion efficiencies (PCEs) exceeding 17% so far.[3−10] Compared to the fused-ring SMA-based systems, all-polymer solar cells (all-PSCs) composed of polymer donor and polymer acceptor materials have some special advantages, such as excellent morphological stability and mechanical properties, which can cater to the requirements of practical application of flexible devices fabricated by roll-to-roll printing techniques.[11−14] Mainly because of the lack of high-performance polymer acceptors, progress toward efficient all-PSCs has been severely constrained, and their corresponding PCEs still lag behind those of fused-ring SMA-based devices. Electron-donating (D1 and D2) moieties forming a 1D/2A or 2D/1A structure in the molecular backbones has been considered as an efficient approach to synergistically optimize the molecular absorption, energy levels, electron mobility, and aggregation of the resulting polymers.[30,38−46] the application of terpolymer acceptors based on two different fused-ring SMA building blocks in all-PSCs has not been reported. The different molecular structures of IDIC16 and ITIC resulted in significantly different solubility, absorption, crystallinity, and aggregation properties.[1,23,47,48] By modulating the IDIC16/ITIC ratios, four nonconjugated terpolymer acceptors (PF1-TS4-xx, where xx is the molar percentage of ITIC unit relative to the total SMA building blocks) were synthesized, and the corresponding optical and electrical properties are conveniently tailored. Matched with a wide band gap polymer donor PM6,49 allPSCs from PF1-TS4-60 achieved a PCE of 9.31% with a high open-circuit voltage (Voc) of 0.99 V, Jsc of 15.30 mA cm−2, and fill factor (FF) of 61.4%, which is ∼50% higher PCE than the copolymer PF1-TS4 based one (6.17%)
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