Ultrafast intramolecular exciton splitting dynamics in isolated low-band-gap polymers and their implications in photovoltaic materials design

Record-setting organic photovoltaic cells with PTB polymers have recently achieved ~8% power conversion efficiencies (PCE). A subset of these polymers, the PTBF series, has a common conjugated backbone with alternating thieno[3,4-b]thiophene and benzodithiophene moieties but differs by the number and position of pendant fluorine atoms attached to the backbone. These electron-withdrawing pendant fluorine atoms fine tune the energetics of the polymers and result in device PCE variations of 2-8%. Using near-IR, ultrafast optical transient absorption (TA) spectroscopy combined with steady-state electrochemical methods we were able to obtain TA signatures not only for the exciton and charge-separated states but also for an intramolecular ("pseudo") charge-transfer state in isolated PTBF polymers in solution, in the absence of the acceptor phenyl-C(61)-butyric acid methyl ester (PCBM) molecules. This led to the discovery of branched pathways for intramolecular, ultrafast exciton splitting to populate (a) the charge-separated states or (b) the intramolecular charge-transfer states on the subpicosecond time scale. Depending on the number and position of the fluorine pendant atoms, the charge-separation/transfer kinetics and their branching ratios vary according to the trend for the electron density distribution in favor of the local charge-separation direction. More importantly, a linear correlation is found between the branching ratio of intramolecular charge transfer and the charge separation of hole-electron pairs in isolated polymers versus the device fill factor and PCE. The origin of this correlation and its implications in materials design and device performance are discussed.     

Synthesis and characterization of new low band‐gap polymers containing electron‐accepting acenaphtho[1,2‐c]thiophene‐S,S‐dioxide groups

Two donor–acceptor conjugated polymers, PTSSO‐TT and PTSSO‐BDT, composed of acenaphtho[1,2‐c]thiophene ‐ S,S‐dioxide (TSSO) as a new electron acceptor and thienothiophene (TT) or benzo[1,2‐b:4,5‐b']dithiophene (BDT) as electron donors, were synthesized with Stille cross‐coupling reactions. The number‐averaged molecular weights (M_n) of PTSSO‐TT and PTSSO‐BDT were found to be 15100 and 26000 Da, with dispersity of 1.8 and 2.4, respectively. The band‐gap energies of PTSSO‐TT and PTSSO‐BDT are 1.56 and 1.59 eV, respectively. The HOMO levels of PTSSO‐TT and PTSSO‐BDT are ?5.4 and ?5.5 eV, respectively. These results indicate that the inclusion of TSSO accepting units into polymers is a very effective method for lowering their HOMO energy levels. The field‐effect mobilities of PTSSO‐TT and PTSSO‐BDT were determined to be 1.5 × 10^?3 and 4.5 × 10^?4 cm² V^?1 s^?1, respectively. A polymer solar cell device prepared with PTSSO‐TT as the active layer was found to exhibit a power conversion efficiency (PCE) of 3.79% with an open circuit voltage of 0.71 V under AM 1.5 G (100 mW cm^?2) conditions. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 498–506     

Enhancement of the Photovoltaic Performance of CH3NH3PbI3 Perovskite Solar Cells through a Dichlorobenzene‐Functionalized Hole‐Transporting Material

A dichlorobenzene‐functionalized hole‐transporting material (HTM) is developed for a CH₃NH₃PbI₃‐based perovskite solar cell. Notwithstanding the similarity of the frontier molecular orbital energy levels, optical properties, and hole mobility between the functionalized HTM [a polymer composed of 2′‐butyloctyl‐4,6‐dibromo‐3‐fluorothieno[3,4‐b]thiophene‐2‐carboxylate (TT‐BO), 3′,4′‐dichlorobenzyl‐4,6‐dibromo‐3‐fluorothieno[3,4‐b]thiophene‐2‐carboxylate (TT‐DCB), and 2,6‐bis(trimethyltin)‐4,8‐bis(2‐ethylhexyloxy)benzo[1,2‐b:4,5‐b′]dithiophene (BDT‐EH), denoted PTB‐DCB21] and the nonfunctionalized polymer [a polymer composed of thieno[3,4‐b]thiophene (TT) and benzo[1,2‐b:4,5‐b′]dithiophene (BDT), denoted PTB‐BO], a higher power conversion efficiency for PTB‐DCB21 (8.7 %) than that for PTB‐BO (7.4 %) is achieved because of a higher photocurrent and voltage. The high efficiency is even obtained without including additives, such as lithium bis(trifluoromethanesulfonyl)imide and/or 4‐tert‐butylpyridine, that are commonly used to improve the conductivity of the HTM. Transient photocurrent–voltage studies show that the PTB‐DCB21‐based device exhibits faster electron transport and slower charge recombination; this might be related to better interfacial contact through intermolecular chemical interactions between the perovskite and the 3,4‐dichlorobenzyl group in PTB‐DCB21.     

Enhanced Charge Transfer,Transport and Photovoltaic Efficiency in All‐Polymer Organic Solar Cells by Polymer Backbone Fluorination

We successfully designed and synthesized two BDT‐BT‐T (BDT=benzo[1,2‐b:4,5‐b']dithiophene, BT‐T=4,7‐dithien‐2‐yl‐2,1,3‐benzothiadiazole) based polymers as the electron donor for application in all‐polymer solar cells (all‐PSCs). By adopting N2200 as the electron acceptor, we systematically investigated the impact of fluorination on the charge transfer, transport, blend morphology and photovoltaic properties of the relevant all‐PSCs. A best power conversion efficiency (PCE) of 3.4% was obtained for fluorinated PT‐BT2F/N2200 (BT2F=difluorobenzo[c][1,2,5]thiadiazole) all‐PSCs in comparison with that of 2.7% in non‐fluorinated PT‐BT/N2200 (BT=benzothiadiazole) based device. Herein, all‐polymers blends adopting either non‐fluorinated PT‐BT or fluorinated PT‐BT2F exhibit similar morphology features. In depth optical spectrum measurements demonstrate that molecular fluorination can further enhance charge transfer between donor and acceptor polymer. Moreover, all‐polymer blends exhibit improved hole mobilities and more balanced carriers transport when adopting fluorinated donor polymer PT‐BT2F. Therefore, although the PCE is relatively low, our findings may become important in understanding how subtle changes in molecular structure impact relevant optoelectronic properties and further improve the performance of all‐PSCSs.     

Tetrathienoanthracene-based copolymers for efficient solar cells

A series of semiconducting copolymers (PTAT-x) containing extended π-conjugated tetrathienoanthracene units have been synthesized. It was shown that the extended conjugation system enhanced the π-π stacking in the polymer/PC(61)BM blend films and facilitated the charge transport in heterojunction solar cell devices. After structural fine-tuning, the polymer with bulky 2-butyloctyl side chains (PTAT-3) exhibited a PCE of 5.6% when it was blended with PC(61)BM.     

Thiadiazoloquinoxaline and benzodithiophene bearing polymers for electrochromic and organic photovoltaic applications

Abstract

Two novel thiadiazoloquinoxaline and benzodithiophene (BDT) bearing copolymers were designed and synthesized. Different BDT units (alkoxy and thiophene substituted) were used as donor materials and the effect of alkoxy and thiophene substitution on the electrochemical, spectroelectrochemical and photovoltaic properties were investigated. Both polymers exhibited low oxidation potentials at around 0.90 V and low optical band gaps at around 1.00?eV due to the insertion of electron poor thiadiazoloquinoxaline unit into the polymer backbone. Both P1 (poly-6,7-bis(3,4-bis(decyloxy)phenyl)-4-(4,8-bis(nonan-3-yloxy)benzo[1,2-b:4,5-b']dithiophen-2-yl)-[1, 2, 5]thiadiazolo[3,4-g]quinoxaline) and P2 (poly- 4-(4,8-bis(5-(nonan-3-yl)thiophen-2-yl)benzo[1,2-b:4,5-b']dithiophen-2-yl)-6,7-bis(3,4-bis(decyloxy)phenyl)-[1, 2, 5]thiadiazolo[3,4-g]quinoxaline) exhibited multichromic behavior with different tones of greenish yellow and gray in the neutral and fully oxidized states, respectively. In addition, both polymers revealed very high optical contrasts (～87%) in the NIR region which make these promising polymers good candidates for NIR applications. Finally, in order to explore the organic photovoltaic performances, P1 and P2 were mixed with PC₇₁BM in the active layer of organic solar cells (OSCs) by conventional device structure. As a result P1 and P2 based devices revealed power conversion efficiencies (PCEs) of 0.33% and 0.60% respectively. However, the additive treatment enhanced PCE from 0.49 to 0.73% for P2 based devices.     

New quinoxaline derivatives as accepting units in donor–acceptor type low‐band gap polymers for organic photovoltaic cells

A series of new donor–acceptor‐type low‐band‐gap semiconducting polymers were synthesized as electron donors for organic photovoltaic cells. The polymers comprised quinoxaline derivatives as the acceptors and a benzodithiophene (BDT) derivative as the donors. 5,8‐Dibromoquinoxaline (Qx), 8,11‐dibromobenzo[a]phenazine (BPz), 10,13‐dibromodibenzo[a,c]phenazine (DBPz), and 8,11‐dibromo‐5‐(9H‐carbazol‐9‐yl)benzo[a]phenazine) (CBPz) were synthesized and polymerized with 2,6‐bis(trimethyltin)?4,8‐diethylhexyloxybenzo‐[1,2‐b;3,4‐b]dithiophene (BDT) through Stille cross‐coupling to produce four types of fully conjugated semiconducting polymers: PBDT‐Qx, PBDT‐BPz, PBDT‐DBPz, and PBDT‐CBPz , respectively. Intramolecular charge transfer between the electron donating and accepting units in the polymeric backbone induced a broad absorption from 300 to 800 nm. The optical band gap energies of the polymers were measured from their absorption onsets to be 1.54–1.80 eV depending on the polymer structure. Solution‐processed field‐effect transistors were fabricated to measure the hole mobilities of the polymers, and bulk hetero‐junction photovoltaic devices were fabricated using the synthesized polymers as electron donors and fullerene derivatives as electron acceptors. One of these devices showed a high power conversion efficiency of 3.87% with an open‐circuit voltage of 0.78 V, a short‐circuit current of 9.68 mA/cm², and a fill factor of 0.51 under air mass 1.5 global (AM 1.5 G) illumination conditions (100 mW/cm²). © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4136–4149     

Pyrrolo[3,4‐c]pyrrole‐1,3‐dione‐based large band gap polymers containing benzodithiophene derivatives for highly efficient simple structured polymer solar cells

Pyrrolo[3,4‐c]pyrrole‐1,3(2H,5H)‐dione (DPPD)‐based large band gap polymers, P(BDT‐TDPPDT) and P(BDTT‐TDPPDT), are prepared by copolymerizing electron‐rich 4,8‐bis(2‐ethylhexyloxy)benzo[1,2‐b:4,5‐b′]dithiophene (BDT) or 4,8‐bis(5‐(2‐ethylhexyl)thiophen‐2‐yl)benzo[1,2‐b:4,5‐b′]dithiophene (BDTT) unit with novel electron deficient 2,5‐dioctyl‐4,6‐di(thiophen‐2‐yl)pyrrolo[3,4‐c]pyrrole‐1,3(2H,5H)‐dione (TDPPDT) unit. The absorption bands of polymers P(BDT‐TDPPDT) and P(BDTT‐TDPPDT) cover the region from 300 to 600 nm with an optical band gap of 2.11 eV and 2.04 eV, respectively. The electrochemical study illustrates that the highest occupied/lowest unoccupied molecular orbital energy levels of P(BDT‐TDPPDT) and P(BDTT‐TDPPDT) are ?5.39 eV/?3.28 eV and ?5.44 eV/?3.40 eV, respectively. The single layer polymer solar cell (PSC) fabricated with a device structure of ITO/PEDOT:PSS/P(BDT‐TDPPDT) or P(BDTT‐TDPPDT):PC70BM+DIO/Al offers a maximum power conversion efficiency (PCE) of 6.74% and 6.57%, respectively. The high photovoltaic parameters such as fill factor (～72%), open circuit voltage (V_oc, ～0.90 V), incident photon to collected electron efficiency (～76%), and PCE obtained for the PSCs made from polymers P(BDT‐TDPPDT) and P(BDTT‐TDPPDT) make them as promising large band gap polymeric candidates for PSC application. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 3564–3574     

Realizing over 10% efficiency in polymer solar cell by device optimization

The low band gap polymer based on benzodithiophene(BDT)-thieno[3,4-b]thiophene(TT)backbone,PBDT-TS1,was synthesized following our previous work and the bulk heterojunction(BHJ)material comprising PBDT-TS1/PC71BM was optimized and characterized.By processing the active layer with different additives i.e.1,8-diiodooctane(DIO),1-chloronaphthalene(CN)and 1,8-octanedithiol(ODT)and optimizing the ratio of each additive in the host solvent,a high PCE of 9.98%was obtained under the condition of utilizing 3%DIO as processing additive in CB.The effect of varied additives on photovoltaic performance was illustrated with atomic force microscopy(AFM)and transmission electron microscope(TEM)measurements that explained changes in photovoltaic parameters.These results provide valuable information of solvent additive choice in device optimization of PBDTTT polymers,and the systematic device optimization could be applied in other efficient photovoltaic polymers.Apparently,this work presents a great advance in single junction PSCs,especially in PSCs with conventional architecture.     

Additive-free non-fullerene organic solar cells with random copolymers as donors over 9% power conversion efficiency

The PBDB-TBT1:ITIC-based device obtains PCE of 9.09%, and is insensitive to additive and thermal annealing, and forms microstructural morphology.     

Thiophene π bridge effect on bulky side‐chained benzodithiophene‐based photovoltaic polymers

Recently, we have used terthiophene side chain to modify benzo[1,2‐b:4,5‐b′]dithiophene (BDT) to form novel building block for BDT polymers. In this paper, this building block is used to copolymerized with thieno[3,4‐c]pyrrole‐4,6‐dione (TPD) and thieno[3,4‐b]thiophene (TT). This building block and TPD‐ or TT‐based polymers (P1 and P3) show high open circuit voltage (V_OC) (ca. 0.9–0.95 V) and low energy loss (E_g–eV_OC) in solar cells devices compared with similar polymers without bulky side chain. We further introduce thiophene π bridge into these polymers backbone to form two other polymers (P2 and P4). We find this thiophene π bridge does contribute to this bulky side chained benzodithiophene polymer photovoltaic performances, especially for power conversion efficiencies (PCEs). The polymer solar cells (PSCs) performances are moderate in this article due to the serious aggregation in the PSCs active layer. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1615–1622     

基于侧链不对称喹喔啉聚合物的高效非富勒烯太阳电池

喹喔啉衍生物由于合成简单,易功能化,成本较低等特点在众多领域都有广泛应用。其自身具有平面刚性结构,也是构建光电聚合物的重要单体。基于喹喔啉单元的有机分子化学结构和电子结构可修饰性强,通过骨架、侧链和取代基等修饰,易于调控分子的能级和吸光光谱,因此,当使用喹喔啉体系的共轭给体与球形富勒烯受体(如PCBM)及弱结晶性非富勒烯受体(如ITIC)均可表现出优异的光伏性能。在本工作中,基于结晶性较强的非富勒烯受体(o-IDTBR),我们首次制备出侧链不对称喹喔啉(简称：不对称喹喔啉)基聚合物(TPQ-1)与之匹配。相比于侧链对称性喹喔啉(简称：对称喹喔啉)(HFQx-T)与o-IDTBR组合,“弱结晶给体-强结晶受体”组合能表现出更佳均匀的相分离尺度,从而获得更高的短路电流及能量转换效率。TPQ-1与o-IDTBR共混后器件效率为8.6%,加入15%的TB7-Th后,器件效率达到9.6%。     

Low‐bandgap quinoxaline‐based D–A‐type copolymers: Synthesis,characterization, and photovoltaic properties

Three classes of quinoxaline (Qx)‐based donor–acceptor (D–A)‐type copolymers, poly[thiophene‐2,5‐diyl‐alt‐2,3‐bis(4‐(octyloxy)phenyl‐quinoxaline‐5,8‐diyl] P(T‐Qx), poly{4,8‐bis(2‐ethylhexyloxy)benzo[1,2‐b:4,5‐b′]dithiophene‐2,6‐diyl‐alt‐2,3‐bis(4‐(octyloxy)phenyl‐quinoxaline‐5,8‐diy} P(BDT‐Qx), and poly{4,8‐bis(2‐ethylhexyloxy)benzo[1,2‐b:4,5‐b′]dithiophene‐2,6‐diyl‐alt‐(5′,8′‐di‐2‐thienyl‐2,3‐bis(4‐octyloxyl)phenyl)‐quinoxaline‐5,5‐diyl} P(BDT‐DTQx), were synthesized via a Stille coupling reaction. The Qx unit was functionalized at the 2‐ and 3‐positions with 4‐(octyloxy)phenyl to provide good solubility and to reduce the steric hindrance. The absorption spectra of the Qx‐containing copolymers could be tuned by incorporating three different electron‐donating moieties. Among these, P(T‐Qx) acted as an electron donor and yielded a high‐performance solar cell by assuming a rigid planar structure, confirmed by differential scanning calorimetry, UV–vis spectrophotometer, and density functional theory study. In contrast, the P(BDT‐Qx)‐based solar cell displayed a lower power conversion efficiency (PCE) with a large torsional angle (34.7°) between the BDT and Qx units. The BDT unit in the P(BDT‐DTQx) backbone acted as a linker and interfered with the formation of charge complexes or quinoidal electronic conformations in a polymer chain. The PCEs of the polymer solar cells based on these copolymers, in combination with [6,6]‐phenyl C70 butyric acid methyl ester (PC₇₁BM), were 3.3% [P(T‐Qx)], 1.9% [P(BDT‐Qx)], and 2.3% [P(BDT‐DTQx)], respectively, under AM 1.5G illumination (100 mW cm^?2). © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

New low band‐gap semiconducting polymers consisting of 5‐(9H‐carbazol‐9‐yl)benzo[a]phenazine as a new acceptor unit for organic photovoltaic cells

A new carbazole‐based electron accepting unit, 5‐(2,7‐dibromo‐9H‐carbazol‐9‐yl)benzo[a]phenazine (CBP), was newly designed and synthesized as the acceptor part of donor‐acceptor type low band‐gap polymers for polymer solar cells. The CBP was copolymerized with electron donating monomers such as benzo[1,2‐b:4,5‐b′]dithiophene (BDT) or 4,8‐bis(2‐octyl‐2‐thienyl)‐benzo[1,2‐b:4,5‐b′]dithiophene (BDTT) through Stille cross‐coupling polymerization, and produced two alternating copolymers, PBDT‐CBP and PBDTT‐CBP. An alternating copolymer (PBDT‐CBZ) consisted of 2,7‐dibromo‐9‐(heptadecan‐9‐yl)‐9H‐carbazole (CBZ) and BDT units was also synthesized for comparison. PBDT‐CBZ showed the maximum absorption at 430 nm and did not show absorption at wavelengths longer than 513 nm. However, CBP containing polymers (PBDT‐CBP and PBDTT‐CBP) showed a broad absorption between 300 and 850 nm due to the intramolecular charge transfer interaction between the electron donating and accepting blocks in the polymeric backbone. Bulk heterojunction photovoltaic devices were fabricated using the synthesized polymers as electron donors and [6,6]‐phenyl C₇₁‐butyric acid methyl ester (PC₇₁BM) as electron acceptor. One of these devices showed a power conversion efficiency of 2.33%, with an open‐circuit voltage of 0.81 V, a short‐circuit current of 6.97 mA/cm², and a fill factor (FF) of 0.41 under air mass (AM) 1.5 global (1.5 G) illumination conditions (100 mW/cm²). © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013, 51, 2354–2365     

Systematic investigation of benzodithiophene- and diketopyrrolopyrrole-based low-bandgap polymers designed for single junction and tandem polymer solar cells

The tandem solar cell architecture is an effective way to harvest a broader part of the solar spectrum and make better use of the photonic energy than the single junction cell. Here, we present the design, synthesis, and characterization of a series of new low bandgap polymers specifically for tandem polymer solar cells. These polymers have a backbone based on the benzodithiophene (BDT) and diketopyrrolopyrrole (DPP) units. Alkylthienyl and alkylphenyl moieties were incorporated onto the BDT unit to form BDTT and BDTP units, respectively; a furan moiety was incorporated onto the DPP unit in place of thiophene to form the FDPP unit. Low bandgap polymers (bandgap = 1.4-1.5 eV) were prepared using BDTT, BDTP, FDPP, and DPP units via Stille-coupling polymerization. These structural modifications lead to polymers with different optical, electrochemical, and electronic properties. Single junction solar cells were fabricated, and the polymer:PC(71)BM active layer morphology was optimized by adding 1,8-diiodooctane (DIO) as an additive. In the single-layer photovoltaic device, they showed power conversion efficiencies (PCEs) of 3-6%. When the polymers were applied in tandem solar cells, PCEs over 8% were reached, demonstrating their great potential for high efficiency tandem polymer solar cells.     

Side chain engineering of naphthalene diimide–bithiophene‐based polymer acceptors in all‐polymer solar cells

Two novel polymeric acceptors based on naphthalene diimide (NDI) and 2.2′‐bithiophene, named as P(NDI2THD‐T2) and P(NDI2TOD‐T2), were designed and synthesized for all polymer solar cells application. The structural and electronic properties of the two acceptors were modulated through side‐chain engineering of the NDI units. The optoelectronic properties of the polymers and the morphologies of the blend films composed of the polymer acceptors and a donor polymer PTB7‐Th were systemically investigated. With thiophene groups introduced into the side chains of the NDI units, both polymers showed wider absorption from 350 nm to 900 nm, compared with the reference polymer acceptor of N2200. No redshift of absorption spectra from solutions to films indicated reduced aggregation of the polymers due to the steric hindrance effect of thiophene rings in the side chains. The photovoltaic performance were characterized for devices in a configuration of ITO/PEDOT:PSS/PTB7‐Th:acceptors/2,9‐bis(3‐(dimethylamino)propyl)anthra[2,1,9‐def:6,5,10‐def]diisoquinoline‐1,3,8,10(2H,9H)‐tetraone (PDIN)/Al. With the addition of diphenyl ether as an additive, the power conversion efficiencies (PCEs) of 2.73% and 4.75% for P(NDI2THD‐T2) and P(NDI2TOD‐T2) based devices were achieved, respectively. The latter showed improved J_sc, Fill Factor (FF), and PCE compared with N2200 based devices. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 3679–3689     

Effects of donor unit and π‐bridge on photovoltaic properties of D–A copolymers based on benzo[1,2‐b:4,5‐c']‐dithiophene‐4,8‐dione acceptor unit

A series of donor‐π‐acceptor (D‐π‐A) conjugated copolymers ( PBDT‐AT, PDTS‐AT, PBDT‐TT , and PDTS‐TT ), based on benzo[1,2‐b:4,5‐c']dithiophene‐4,8‐dione (BDD) acceptor unit with benzodithiophene (BDT) or dithienosilole (DTS) as donor unit, alkylthiophene (AT) or thieno[3,2‐b]thiophene (TT) as conjugated π‐bridge, were designed and synthesized for application as donor materials in polymer solar cells (PSCs). Effects of the donor unit and π‐bridge on the optical and electrochemical properties, hole mobilities, and photovoltaic performance of the D‐π‐A copolymers were investigated. PSCs with the polymers as donor and PC₇₀BM as acceptor exhibit an initial power conversion efficiency (PCE) of 5.46% for PBDT‐AT , 2.62% for PDTS‐AT , 0.82% for PBDT‐TT , and 2.38% for PDTS‐TT . After methanol treatment, the PCE was increased up to 5.91%, 3.06%, 1.45%, and 2.45% for PBDT‐AT, PDTS‐AT, PBDT‐TT , and PDTS‐TT , respectively, with significantly increased FF. The effects of methanol treatment on the photovoltaic performance of the PSCs can be ascribed to the increased and balanced carrier transport and the formation of better nanoscaled interpenetrating network in the active layer. The results indicate that both donor unit and π‐bridge are crucial in designing a D‐π‐A copolymer for high‐performance photovoltaic materials. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1929–1940     

A New D–A conjugated polymer P(PTQD‐BDT) with PTQD acceptor and BDT donor units for BHJ polymer solar cells application

A novel donor–acceptor ( D–A ) copolymer comprising of weak electron donating BDT moiety and strong 9‐(2‐octyldodecyl)?8H‐pyrrolo[3,4‐b] bisthieno[2,3‐f:3',2'‐h] quinoxaline‐8,10(9H)‐dione (PTQD) unit denoted as P(PTQD‐BDT) was synthesized as donor material for polymer solar cells. P(PTQD‐BDT) shows a broad visible‐near‐infrared absorption band with an optical bandgap of 1.74 eV and possesses a relatively low‐lying HOMO level at ?5.28 eV. Bulk‐heterojunction polymer solar cell with the optimized blend of 1:2 (weight ratio) P(PTQD‐BDT):PC₇₁BM (processed with chloroform) shows an open circuit voltage of 0.92 V, a short circuit current density of 7.84 mA/cm², and a fill factor of 0.50, achieving a power conversion efficiency (PCE) of 3.61%. The PCE has been further improved to 5.55 % (J_sc = 10.34 mA/cm², V_oc = 0.88V and FF = 0.61), when 3% v ol 1,8‐diio‐dooctane (DIO) was used as solvent additive for the processing of P(PTQD‐BDT):PC₇₁BM blended film. The enhancement in J_sc is as a result of the appropriate morphology and efficient exciton dissociation into free charge carrier. The increase in PCE has been attributed to the favorable nanoscale morphology for efficient exciton dissociation and charge transport (reduction in the electron to hole mobility ratio). © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2390–2398     

Inverted polymer solar cells with Zn2SnO4 nanoparticles as the electron extraction layer

In this study, we report narrow-size distribution Zn₂SnO₄ (ZSO) nanoparticles, which are produced by low-temperature solution-processed used as the electron extraction layer (EEL) in the inverted polymer solar cells (i-PSCs). Moreover, poly[(9,9-bis(3'-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)] (PFN) is used to modify the surface properties of ZSO thin film. By using the ZSO NPs/PFN as the EEL, the i-PSCs fabricated by poly[4,8-bis(2-ethylhexyloxyl)benzo[1,2-b:4,5-b'] dithio-phene-2,6-diyl-altethylhexyl-3-fluorothithieno [3,4-b]thiophene-2-carboxylate-4,6-diyl] (PTB7) blended with (6,6)-phenyl-C₇₁-butyric acid methylester (PC₇₁BM) bulk heterojunction (BHJ) composite, exhibits a power conversion efficiency (PCE) of 8.44%, which is nearly 10% enhancement as compared with that of 7.75% observed from the i-PSCs by PTB7:PC₇₁BM BHJ composite using the ZnO/PFN EEL. The enhanced PCE is originated from improved interfacial contact between the EEL with BHJ active layer and good energy level alignment between BHJ active layer and the EEL. Our results indicate that we provide a simple way to boost efficiency of i-PSCs.     

新型基于二氟苯并噻二唑和双噻吩丙烯腈共轭聚合物的设计、合成及光伏性能

设计并合成了两种基于5,6-二氟苯并噻二唑和双噻吩丙烯腈单元的D-A型共轭聚合物,聚[(5,6-二氟-苯[c][1,2,5]噻二唑-4,7-基)-交替-((E)-2,3-双(3'-(2-辛基十二烷基)-(2,2'-双噻吩)-5,5'-基)丙烯腈)](DFBT812)和聚[(5,6-二氟-苯[c][1,2,5]噻二唑-4,7-基)-交替-((E)-2,3-双(3'-(2-癸基十四烷基)-(2,2'-双噻吩)-5,5'-基)丙烯腈)](DFBT1014)作为聚合物太阳电池的给体材料。通过侧链工程,引入了2-辛基十二烷基和2-癸基十四烷基侧链实现对聚合物的溶解性,结晶性以及共混膜形貌的调节。研究结果表明,共轭聚合物DFBT812与PC_(61)BM的共混膜表现出更好的相分离尺度,能够促进载流子的传输和抽取。基于共轭聚合物DFBT812的太阳电池器件取得了0.87 V的开路电压和6.25%的能量转换效率。除此之外,基于DFBT812的聚合物太阳电池器件在活性层厚度为220 nm时仍然表现出6%的能量转换效率。