Property modulation of dithienosilole-based polymers via the incorporation of structural isomers of imide- and lactam-functionalized pyrrolo[3,4-c]pyrrole units for polymer solar cells

doi:10.1016/j.polymer.2015.03.078

Polymer

Volume 65, 18 May 2015, Pages 243-252

https://doi.org/10.1016/j.polymer.2015.03.078 Get rights and content

Highlights

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Polymers containing imide- or lactam-functionalized pyrrolopyrroles were prepared.
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Imide-functionalized polymer displayed large band gap and deep HOMO level.
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Lactam-functionalized polymer showed low band gap and high HOMO level.
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Imide- and lactam-functionalized polymers showed similar hole mobilities.
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Imide- and lactam-functionalized polymers afforded a PCE of 3.46% and 3.60%.

Abstract

Three new electron rich dithienosilole (DTS)-based polymers (P1, P2 and P3) incorporating electron deficient imide-functionalized pyrrolo[3,4-c]pyrrole-1,3-dione (DPPD), lactam-functionalized pyrrolo[3,4-c]pyrrole-1,4-dione (DPP) or both of DPPD and DPP units were prepared to study the property modulation of polymers via functional group inter-conversion in their main chain. The intense absorption of P1 incorporating DPPD covered the region, 300 nm–650 nm, with the maximum absorption at 526 nm, while P2 incorporating DPP showed a strong absorption band between 500 nm and 950 nm with the maximum absorption at 733 nm. Interestingly, P3 incorporating both of DPPD and DPP units displays broad absorption from 300 nm to 950 nm with two distinct characteristic absorption maxima at 518 nm and 731 nm. The estimated optical band gaps of P1–P3 were 1.91 eV, 1.31 eV and 1.35 eV, respectively. The highest occupied molecular orbital (HOMO) energy levels of P1–P3 are observed at −5.36 eV, −5.07 eV and −5.12 eV, respectively. An examination of the organic field effect transistors (OFETs) prepared with each of P1–P3 showed that P1 exhibits higher hole mobility (μ) of 2.7 × 10⁻⁴ cm²V⁻¹ s⁻¹ compared to that of P2 (1.3 × 10⁻⁴ cm² V⁻¹ s⁻¹) and P3 (7.0 × 10⁻⁵ cm² V⁻¹ s⁻¹). The polymer soar cells (PSCs) made from each of polymers P1–P3 as a donor and PC₇₀BM as an acceptor with the simple device structure of ITO/PEDOT:PSS/polymer:PC₇₀BM + DIO/Al produced a maximum power conversion efficiency (PCE) of 3.46%, 3.60% and 0.93%, respectively.

Graphical abstract

Introduction

Bulk heterojunction (BHJ) solar cells prepared from organic semiconducting materials are considered the most promising solar to electrical energy conversion techniques because of their easy device fabrication over large areas at low cost [1]. Polymer-based BHJ solar cells (PSCs) fabricated with electron donating π-conjugated polymers and electron accepting fullerene derivatives were reported to display impressive power conversion efficiency (PCE) of 10.5% [2], [3] and 11.5% [4] for single and multilayer PSCs, respectively. In recent years, numerous π-conjugated polymers [5], [6], [7], [8], [9], [10] and fullerene derivatives [11], [12], [13] have been developed to produce highly efficient PSCs because the photovoltaic performance of PSCs is strongly influenced by the properties of the donor and acceptor materials used in the photoactive layer. For example, many π-conjugated polymers possessing deep highest occupied molecular orbital (HOMO) level [14], [15], [16] and fullerene derivatives [11], [12], [13] or electron accepting organic small molecules [13], [17] showing high lowest unoccupied molecular (LUMO) orbital level have been developed to obtain a high open circuit voltage (V_oc). In addition, several low band gap donor-acceptor (D-A) polymers incorporating bridged electron rich units, such as cyclopentadithiophene (CPDT), benzodithiophene (BDT) and dithienosilole (DTS), and electron accepting benzo[c][1,2,5]thiadiazole (BT), thieno[3,4-b]thiophene (TT), thieno[3,4-c]pyrrole-4,6-dione (TPD), isoindigo (ID), and diketo-pyrrolo[3,4-c]pyrrole-1,4-dione (DPP) units were reported to obtain a high current density (J_sc) and fill factor (FF) because J_sc and FF of the PSCs are strongly influenced by the light harvesting ability and the carrier mobility of the polymers [5], [6], [7], [8], [9], [10]. All of these studies showed that the PCE of PSCs is enhanced remarkably when the suitable electron donor and acceptor are used in the preparation of PSCs.

Recently, a novel electron accepting pyrrole-based imide-functionalized pyrrolo[3,4-c]pyrrole-1,3-dione (DPPD) derivative, which is the structural isomer of lactam-functionalized pyrrolo[3,4-c]pyrrole-1,4-dione (DPP) unit, was prepared to make a new D-A polymer for PSCs [18], [19], [20], [21]. The DPPD-based polymer incorporating an electron rich benzodithiophene (BDT) derivative displayed impressive photovoltaic properties though their band gap (∼2.11 eV) was relatively higher than that of most promising poly(3-hexylthiophene) [19]. The chemical structure of high energy converting DPPD-based large polymer, P(BDT-TDPPDT), is presented in Fig. 1. It should be noted that the PSC made from P(BDT-TDPPDT) not only showed a high PCE of 6.74%, but also displayed impressive photovoltaic parameters, such as high V_oc (0.90 V), FF (72%), incident photon to current efficiency (IPCE_max, 76%) and reasonable J_sc (10.94 mA/cm²) [19]. The V_oc and FF values are high enough, but the relatively low J_sc value because of its wide band gap limits the overall performance of P(BDT-TDPPDT). As stated earlier, to increase the J_sc further, it is important to lower the band gap. To achieve this aim, thiophene-based imide-functionalized thieno[3,4-c]pyrrole-4,6-dione (TPD) was incorporated in the P(BDT-TDPPDT) main chain via random copolymerization [20]. As expected, the band gap of the random polymer was lowered by ∼0.2 eV compared to that of P(BDT-TDPPDT). Consequently, the random polymer gave a higher J_sc (∼11.52 mA/cm²) and PCE (∼7.01%) than P(BDT-TDPPDT) [20].

Another simple way to lower the band gap of DPPD-based polymer is to copolymerize it with a different electron donor unit. Note that the polymer (PDTSTPD) shown in Fig. 1 containing thiophene-based imide-functionalized thieno[3,4-c]pyrrole-4,6-dione (TPD) and electron rich dithienosilole (DTS) [22], [23], [24], [25] displayed relatively a lower band gap (∼1.73 eV) and higher PCE than the polymer containing BDT and TPD [26], [27], [28]. In this instance, DPPD was copolymerized with DTS derivative to produce a new D-A polymer, P1, which is expected to show a lower band gap than P(BDT-TDPPDT). In addition, to compare the properties of P1 with its structural isomer, P2 was prepared via the polymerization between DTS and DPP. Random polymer P3 was also synthesized by random copolymerization between DTS, DPPD and DPP derivatives to understand the property changes compared to those of its respective alternating polymers P1 and P2. Here, we wish to report the synthesis of three new polymers P1, P2 and P3 and their optical, electrochemical, charge transport and photovoltaic properties. In addition, we briefly studied their property modulation via the incorporation of differently functionalized pyrrolo[3,4-c]pyrrole units.

Section snippets

Materials and instruments

All the necessary reagents and solvents were obtained from Sigma–Aldrich or TCI chemicals. The electron rich co-monomer, 4,4′-bis(octyl)-5,5′-bis(trimethyltin)-dithieno[3,2-b:2′,3′-d]silole (DTS), was purchased from Suna Tech Inc (Cat no # IN1257, purity ∼ 97%). The purification of the new compounds was performed by column chromatography (silica gel, Merck Kieselgel 60, 70–230 mesh ASTM). The nuclear magnetic resonance (NMR) spectra of the compounds and polymers were recorded on Varian Mercury

Synthesis and characterization of polymers

The monomer DPPD was prepared, as shown in Scheme 1, via a more facile route than the procedure reported recently [19]. The incorporation of bromides on compound 1 makes the purification easier and avoids the chlorination at the 5-position of thiophene at the final stage of the thionyl chloride (SOCl₂) treatment. Earlier, chlorination at the 5-position of the thiophene units was observed when there were no bromides [19]. On the other hand, monomer DPP was prepared using the reported procedures

Conclusions

Three new dithienosilole (DTS)-based polymers incorporating structural isomers of imide-functionalized pyrrolo[3,4-c]pyrrole-1,3-dione (DPPD) derivative, lactam-functionalized pyrrolo[3,4-c]pyrrole-1,4-dione (DPP) derivative or both DPPD and DPP derivatives in their main chain were prepared. The imide-functionalized polymer P1 showed a narrow absorption band in the range of 300–650 nm with a band gap of 1.91 eV, whereas the lactam-functionalized P2 exhibited a lower band gap of 1.31 eV with

Acknowledgments

This research was supported by the National Research Foundation of Korea (NRF-2013R1A2A2A04014576). S.C. acknowledges the support by the Priority Research Centers Program (2009-0093818) at the University of Ulsan.

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The reagents were obtained from Sigma-Aldrich, and polymer P4, namely poly([2,6′-4,8-di(5-ethylhexylthienyl)benzo[1,2-b; 3,3-b]dithiophene]{3-fluoro-2[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl}), was obtained from Organic Nano Electronic (ONE = 1) Materials. The monomers 2,6-bis(trimethyltin)-4,8-bis(2-ethylhexyloxy)benzo[1,2-b:4,5-bʹ]dithiophene (BDT) [54], 4,6-bis(5-bromothiophen-2-yl)-2,5-dioctylpyrrolo[3,4-c]pyrrole-1,3(2H,5H)-dione (PPD) [54,56], and 4,7-bis(5-bromo-4-octylthiophen-2-yl)-5,6-difluorobenzo[c] [1,2,5]thiadiazole (DTffBT) [56] were prepared according to the literature. The molecular weights were measured on an Agilent 1200 Infinity Series separation module.
A new approach is presented here to maximize the efficiency of ternary blend polymer solar cells (ter-PSCs). The properties of co-absorbing wide band-gap polymers are fine-tuned via the insertion of two different appropriate electron-acceptor units on their backbone in different ratios, and the resulting polymers are utilized as a co-absorbent on ter-PSCs. The copolymerization of benzodithiophene, pyrrolopyrrole-1,3-dione, and difluoro-benzothiadiazole derivatives at three different ratios, 1.00:1.00:0.00, 1.00:0.50:0.50, and 1.00:0.25:0.75, produces the polymers P1–P3. The absorption bands of P1–P3 are gradually red-shifted, and the band-gaps are reduced. The crystallinity of the polymers is increased in the order of P1 < P2 < P3. The binary polymer solar cells (bi-PSCs) are fabricated using blends of P1, P2, or P3 with PC₇₀BM and provide comparable power conversion efficiencies (PCEs) of 5.41%, 5.55%, and 4.01%, respectively. However, the inclusion of 20 wt% of each of P1, P2, and P3 on a P4 (=PTB7-Th):PC₇₀BM blend offers PCEs of 9.31%, 9.60%, and 9.85%, respectively, which are higher than that of the bi-PSC made using a blend of P4:PC₇₀BM (PCE = 8.20%). The improved absorption, crystallinity, and carrier mobilities of the ternary blends are the main reasons for their enhanced photovoltaic performance compared with the binary blends.
Effects of replacing benzodithiophene with a benzothiadiazole derivative on an efficient wide band-gap benzodithiophene-alt-pyrrolo[3,4-c]pyrrole-1,3(2H,5H)-dione copolymer
2019, Journal of Photochemistry and Photobiology A: Chemistry
Citation Excerpt :
A new monomer and polymer have been synthesized via the route shown in Scheme 1. Monomer PPD was prepared by treating PPD-anhydride[28] with 2-octyldodecan-1-amine, followed by thionyl chloride. The conventional Stille polymerization between monomers PPD and DTBT-derived polymer P(DTBT-PPD), with high yield.
In this study, we investigated the property modulation of a high energy converting, wide-band-gap, alternating polymer, P(BDTT-PPD), comprising benzodithiophene (BDTT) and pyrrolo[3,4-c]pyrrole-1,3(2H,5H)-dione (PPD) derivatives by replacing BDTT with 4,7-di(thiophen-2-yl)benzo[c][1,2,5]thiadiazole (DTBT). The new alternating polymer, named P(DTBT-PPD), was prepared by polymerizing distannyl DTBT and dibromo PPD derivatives, with the aim of making a PPD-based, low-band-gap polymer for solar cell applications. Polymer P(DTBT-PPD) displayed an intense absorption band between 300 and 750 nm with two distinct absorption maxima at 439 and 605 nm as a film. The calculated optical band-gap (E_g) was 1.64 eV. The determined highest occupied and lowest unoccupied molecular (HOMO and LUMO, respectively) orbital energy levels of P(DTBT-PPD) were −5.30 and −3.66 eV, respectively. Solution-processed organic solar cells (OSCs), made with P(DTBT-PPD):PC₇₀BM ([6,6]-Phenyl C₇₁ butyric acid methyl ester), provided a maximum power-conversion efficiency (PCE) of 2.23%. P(DTBT-PPD) displayed much lower E_g (≈0.4 eV), slightly higher HOMO level (≈0.14 eV), and considerably lower PCE (≈4%), than P(BDTT-PPD). The increased curvature of P(DTBT-PPD) chains could be the main reason for their lower PCE than P(BDTT-PPD).
Thiophene and thieno[3,2-b]thiophene π-bridged pyrrolo[3,4-c]pyrrole-1,3-dione-based wide band-gap polymers for fullerene and non-fullerene organic solar cells
2018, Organic Electronics
The conventional polymerization of 2,5-bis(trimethylstannyl)thiophene (T) or 2,5-bis(trimethylstannyl)thieno[3,2-b]thiophene (Tt) with 4,6-bis(5-bromothiophen-2-yl)-5-octyl-2-(2-octyldodecyl)pyrrolo[3,4-c]pyrrole-1,3(2H,5H)-dione (TPPDT) afforded new alternating polymers, namely P(T-TPPDT) or P(Tt-TPPDT), respectively. Both P(T-TPPDT) and P(Tt-TPPDT) exhibited similar thermal stabilities (5% weight loss at around 420 °C) and absorption maxima (λ_max ≈ 515 nm) as films. The absorption bands of P(T-TPPDT) and P(Tt-TPPDT) extend between 300 and 620 nm, with optical band gaps (E_gs) of 2.02 eV and 2.00 eV, respectively. The highest-occupied/lowest-unoccupied molecular-orbital energies of P(Tt-TPPDT) (HOMO/LUMO: −5.35 eV/–3.33 eV) were found to be somewhat higher than those of P(T-TPPDT) (HOMO/LUMO: −5.31 eV/–3.31 eV). Organic solar cells (OSCs) prepared using 1:1.5 (w/w) P(T-TPPDT):PC₇₀BM or P(Tt-TPPDT):PC₇₀BM (PC₇₀BM = [6,6]-phenyl C₇₀ butyric acid methyl ester) blends provided power-conversion efficiencies (PCEs) of 3.50% or 4.71%, respectively. On the other hand, OSCs prepared with 1:1 (w/w) P(T-TPPDT):ITIC or P(Tt-TPPDT):ITIC (ITIC = 3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)indanone))-5,5,11,11-tetrakis(4-hexylphenyl)dithieno[2,3-d:2′,3′-d’]-s-indaceno[1,2-b:5,6-b’]dithiophene) blends exhibited improved PCEs of 5.32% or 6.35%, respectively.
Benzodithiophene based ternary copolymer containing covalently bonded pyrrolo[3,4-c]pyrrole-1,3-dione and benzothiadiazole for efficient polymer solar cells utilizing high energy sunlight
2016, Organic Electronics
Citation Excerpt :
The synthetic route to a new electron deficient monomer, PDBT, and ternary copolymer, P(BDTT-PDBT), is shown in Scheme 1. The key intermediate 1 was synthesized using the reported synthetic procedures [17,20], and subjected to mono-bromination using NBS to obtain mono-brominated product 2, but a mixture of un-reacted 1, expected mono-brominated product 2 and a di-brominated compound was obtained. Careful column chromatography offered pure compound 2.
A new electron deficient monomer (PDBT) unit incorporating a weak electron accepting unit, pyrrolo[3,4-c]pyrrole-1,3-dione (DPPD), and a strong electron accepting unit, 4,7-di(thiophen-2-yl)benzo[c][1,2,5]thiadiazole (BT), with a configuration of DPPD-BT-DPPD was prepared, and copolymerized with a benzodithiophene (BDTT) derivative to afford a new alternating ternary copolymer P(BDTT-PDBT). The estimated optical band gap (E_g) and highest occupied/lowest unoccupied (HOMO/LUMO) molecular orbital energy levels of P(BDTT-PDBT) were 1.72 eV and −5.45 eV/−3.62 eV, respectively. A field effect transistor made from P(BDTT-PDBT) exhibited a hole mobility of 3.2 × 10⁻³ cm² V⁻¹ s⁻¹. Conventional single layer polymer solar cells (PSCs) prepared using P(BDTT-PDBT) with an additive offered a maximum power conversion efficiency (PCE) of 5.73% with an open-circuit voltage (V_oc) of 0.90 V, a short-circuit current (J_sc) of 9.73 mA/cm², and a fill factor (FF) of 0.66. Interestingly, the PSC device prepared without an additive also showed a similar PCE of 4.84% (V_oc ∼ 0.92 V, J_sc ∼ 8.08 mA/cm², and FF ∼ 0.65). This paper reports the preparation of an efficient ternary copolymer for polymer solar cells utilizing high energy sunlight, as well as the property modulation of an alternating binary copolymer, P(BDTT-DPPD), containing BDTT and DPPD derivatives via the insertion of a strong electron accepting BT unit on the P(BDTT-DPPD) backbone.
Imide-linked alkyl chain influence on the properties of pyrrole-based imide-functionalized polymers containing pyrrolo[3,4-c]pyrrole-1,3(2H,5H)-dione and benzodithiophene units for polymer solar cells
2016, Synthetic Metals
A series of pyrrolo[3,4-c]pyrrole-1,3(2H,5H)-dione (DPPD)-based polymers incorporating different alkyl side chains on the imide nitrogen were prepared to investigate the imide-linked alkyl side chain effects on the properties of DPPD-based polymers. DPPD derivatives with heptyl, octyl, decyl and dodecyl substituents on the imide nitrogen were prepared and copolymerized with 2,6-bis(trimethyltin)-4,8-bis(2-ethylhexyloxy)benzo[1,2-b:4,5-b′]dithiophene (BDT) to offer polymers P(BDT-C₇-DPPD), P(BDT-C₈-DPPD), P(BDT-C₁₀-DPPD), and P(BDT-C₁₂-DPPD), respectively. All four polymers displayed identical optical band gaps (E_g ∼ 2.11 eV) and highest occupied/lowest unoccupied molecular orbital energy levels (HOMO/LUMO ∼ −5.39 eV/–3.28 eV). The conventional single layer polymer solar cell (PSC) fabricated with a device structure of ITO/PEDOT:PSS/polymer:PC₇₀BM (1:1.5 wt%)/Al offered a power conversion efficiency (PCE) of 1.65%, 1.49%, 1.24%, and 0.87%, respectively. The PSC device performance was improved to 5.67%, 5.29%, 4.06%, and 2.46%, respectively, with the use of processive additive such as 1,8-diiodoocate (DIO).

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Property modulation of dithienosilole-based polymers via the incorporation of structural isomers of imide- and lactam-functionalized pyrrolo[3,4-c]pyrrole units for polymer solar cells

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Materials and instruments

Synthesis and characterization of polymers

Conclusions

Acknowledgments

Mater Today

Prog Polym Sci

Sol Energy Mater Sol Cells

Polymer

Synt Met

Nat Commun

Adv Mater

Adv Mater

Chem Rev

Prog Polym Sci

Polym Chem

Polym Chem

Polym Chem

Energy Environ Sci

J Nanosci Nanotechnol

EPJ Photovolt