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     

Modulation of electronic properties of π‐conjugated copolymers derived from naphtho[1,2‐b:5,6‐b′]dithiophene donor unit: A structure‐property relationship study

A set of three donor‐acceptor conjugated (D‐A) copolymers were designed and synthesized via Stille cross‐coupling reactions with the aim of modulating the optical and electronic properties of a newly emerged naphtho[1,2‐b:5,6‐b′]dithiophene donor unit for polymer solar cell (PSCs) applications. The PTNDTT‐BT , PTNDTT‐BTz , and PTNDTT‐DPP polymers incorporated naphtho[1,2‐b:5,6‐b′]dithiophene ( NDT ) as the donor and 2,2′‐bithiazole ( BTz ), benzo[1,2,5]thiadiazole ( BT ), and pyrrolo[3,4‐c]pyrrole‐1,4(2H,5H)‐dione ( DPP ), as the acceptor units. A number of experimental techniques such as differential scanning calorimetry, thermogravimetry, UV–vis absorption spectroscopy, cyclic voltammetry, X‐ray diffraction, and atomic force microscopy were used to determine the thermal, optical, electrochemical, and morphological properties of the copolymers. By introducing acceptors of varying electron withdrawing strengths, the optical band gaps of these copolymers were effectively tuned between 1.58 and 1.9 eV and their HOMO and LUMO energy levels were varied between ?5.14 to ?5.26 eV and ?3.13 to ?3.5 eV, respectively. The spin‐coated polymer thin film exhibited p‐channel field‐effect transistor properties with hole mobilities of 2.73 × 10^?3 to 7.9 × 10^?5 cm² V^?1 s^?1. Initial bulk‐heterojunction PSCs fabricated using the copolymers as electron donor materials and [6,6]‐phenyl C71 butyric acid methyl ester (PC₇₁BM) as the acceptor resulted in power conversion efficiencies in the range of 0.67–1.67%. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2948–2958     

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.     

Using Cyclopenta[2,1‐b:3,4‐c′]dithiophene‐4‐one as a Building Block for Low‐Bandgap Conjugated Copolymers Applied in Solar Cells

A novel electron‐accepting unit cyclopenta[2,1‐b:3,4‐c′]dithiophene‐4‐one (CPDTO‐c′), which is an isomer of CPDTO‐b′ was developed. CPDTO‐c′ can be incorporated into the D–A backbone through 5, 7 positions. The 2 position of CPDTO‐c′ can be easily functionalized with an electron‐withdrawing chain. By copolymerizing CPDTO‐c′ with four different donor units: benzo[1,2‐b:4,5‐b′]dithiophene (BDT), dithieno[3,2‐b:2′,3′‐d]silole (DTS), carbazole, and fluorene, four new conjugated copolymers P1 – P4 were obtained. All these polymers have good solubility and low‐lying HOMO energy levels (−5.41 ∼ −5.92 eV). Among them, P1 and P2 exhibit broad absorption and narrow optical bandgaps of 1.91 and 1.72 eV, respectively. Solar cells based on P1 /PC₇₁BM afforded a PCE up to 2.72% and a high V_oc up to ∼0.9 V.     

Synthesis and Photovoltaic Properties of Cyclopentadithiophene‐Based Low‐Bandgap Copolymers That Contain Electron‐Withdrawing Thiazole Derivatives

We have synthesized four types of cyclopentadithiophene (CDT)‐based low‐bandgap copolymers, poly[{4,4‐bis(2‐ethylhexyl)‐4H‐cyclopenta[2,1‐b:3,4‐b′]dithiophene‐2,6‐diyl}‐alt‐(2,2′‐bithiazole‐5,5′‐diyl)] ( PehCDT‐BT ), poly[(4,4‐dioctyl‐4H‐cyclopenta[2,1‐b:3,4‐b′]dithiophene‐2,6‐diyl)‐alt‐(2,2′‐bithiazole‐5,5′‐diyl)] ( PocCDT‐BT ), poly[{4,4‐bis(2‐ethylhexyl)‐4H‐cyclopenta[2,1‐b:3,4‐b′]dithiophene‐2,6‐diyl}‐alt‐{2,5‐di(thiophen‐2‐yl)thiazolo[5,4‐d]thiazole‐5,5′‐diyl}] ( PehCDT‐TZ ), and poly[(4,4‐dioctyl‐4H‐cyclopenta[2,1‐b:3,4‐b′]dithiophene‐2,6‐diyl)‐alt‐{2,5‐di(thiophen‐2‐yl)thiazolo[5,4‐d]thiazole‐5,5′‐diyl}] ( PocCDT‐TZ ), for use in photovoltaic applications. The intramolecular charge‐transfer interaction between the electron‐sufficient CDT unit and electron‐deficient bithiazole (BT) or thiazolothiazole (TZ) units in the polymeric backbone induced a low bandgap and broad absorption that covered 300 nm to 700–800 nm. The optical bandgap was measured to be around 1.9 eV for PehCDT‐BT and PocCDT‐BT , and around 1.8 eV for PehCDT‐TZ and PocCDT‐TZ . Gel permeation chromatography showed that number‐average molecular weights ranged from 8000 to 14 000 g mol^?1. Field‐effect mobility measurements showed hole mobility of 10^?6–10^?4 cm² V^?1 s^?1 for the copolymers. The film morphology of the bulk heterojunction mixtures with [6,6]phenyl‐C₆₁‐butyric acid methyl ester (PCBM) was also examined by atomic force microscopy before and after heat treatment. When the polymers were blended with PCBM, PehCDT‐TZ exhibited the best performance with an open circuit voltage of 0.69 V, short‐circuit current of 7.14 mA cm^?2, and power conversion efficiency of 2.23 % under air mass (AM) 1.5 global (1.5 G) illumination conditions (100 mW cm^?2).     

Synthesis and photovoltaic investigation of dithieno[2,3‐d:2′,3′‐d′]‐benzo[1,2‐b:3,4‐b′:5,6‐d″]trithiophene‐based conjugated polymer with an enlarged π‐conjugated system

Compared with benzo[1,2‐b:3,4‐b′:5,6‐d″]trithiophene (BTT), an extended π‐conjugation fused ring derivative, dithieno[2,3‐d:2′,3′‐d′]benzo[1,2‐b:3,4‐b′:5,6‐d″]trithiophene (DTBTT) has been designed and synthesized successfully. For investigating the effect of extending conjugation, two wide‐bandgap (WBG) benzo[1,2‐b:4,5‐b′]dithiophene (BDT)‐based conjugated polymers (CPs), PBDT‐DTBTT, and PBDT‐BTT, which were coupled between alkylthienyl‐substituted benzo[1,2‐b:4,5‐b′]dithiophene bistin (BDT‐TSn) and the weaker electron‐deficient dibromides DTBTTBr₂ and BTTBr₂ bearing alkylacyl group, were prepared. The comparison result revealed that the extending of conjugated length and enlarging of conjugated planarity in DTBTT unit endowed the polymer with a wider and stronger absorption, more ordered molecular structure, more planar and larger molecular configuration, and thus higher hole mobility in spite of raised highest occupied molecular orbital (HOMO) energy level. The best photovoltaic devices exhibited that PBDT‐DTBTT/PC₇₁BM showed the power conversion efficiency (PCE) of 2.73% with an open‐circuit voltage (V_OC) of 0.82 V, short‐circuit current density (J_SC) of 6.29 mA cm^?2, and fill factor (FF) of 52.45%, whereas control PBDT‐BTT/PC₇₁BM exhibited a PCE of 1.98% under the same experimental conditions. The 38% enhanced PCE was mainly benefited from improved absorption, and enhanced hole mobility after the conjugated system was extended from BTT to DTBTT. Therefore, our results demonstrated that extending the π‐conjugated system of donor polymer backbone was an effective strategy of tuning optical electronic property and promoting the photovoltaic property in design of WBG donor materials.     

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     

Photodegradation of C‐PCPDTBT and Si‐PCPDTBT: Influence of the Bridging Atom on the Stability of a Low‐Band‐Gap Polymer for Solar Cell Application

The kinetics of photodegradation and the reactivity of different sites of the low‐band‐gap polymers poly[2,6‐(4,4‐bis‐(2‐ethylhexyl)‐4H‐cyclopenta[2,1‐b:3,4‐b′]dithiophene)‐alt‐4,7‐(2,1,3‐benzothiadiazole)] (C‐PCPDTBT) and poly[2,6‐(4,4‐bis‐(2‐ethylhexyl)dithieno[3,2‐b:2′,3′‐d]silole)‐alt‐4,7‐(2,1,3‐benzothiadiazole)] (Si‐PCPDTBT) are investigated as thin films and are compared to those of poly(3‐hexylthiophene) (P3HT). The decay kinetics are monitored with UV/Vis spectroscopy and the reactivity and product evolution are investigated with X‐ray photoelectron spectroscopy (XPS). Both polymers exhibit higher stability than P3HT. The bridging atom in the cyclopentadithiophene (CPDT) subunit has a significant influence on the stability. Varying oxidation rates for the different elements were observed. In the case of Si‐PCPDTBT, the silicon atom is oxidized primarily, whereas the photooxidation rates of the other elements are reduced relative to C‐PCPDTBT. Additionally, XPS experiments with varying excitation energies reveal a significant reaction gradient within a few nanometers of the surface of degraded thin films of C‐PCPDTBT.     

Dithienobenzimidazole‐containing conjugated donor–acceptor polymers: Synthesis and characterization

The synthesis of two new conjugated polymers based on the relatively under‐exploited monomer, 5,8‐dibromo‐2‐[5‐(2‐hexyldecyl)‐2‐thienyl]‐1H‐dithieno[3,2‐e:2′,3′‐g]benzimidazole (dithienobenzimidazole, DTBI ), and either 4,7‐bis[4‐hexyl‐5‐(trimethylstannyl)‐2‐thienyl]‐2,1,3‐benzothiadiazole ( BTD ) or 2,6‐bis(trimethylstannyl)‐4,8‐bis(5‐(2‐ethylhexyl) thiophen‐2‐yl)benzo[1,2‐b:4,5‐b′]dithiophene ( BDT ) is described. The polymers were synthesized via Stille polycondensation and characterized by traditional methods (¹H NMR, gel‐permeation chromatography, matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry, thermal gravimetric analysis, differential scanning calorimetry, ultraviolet–visible spectroscopy, photoluminescence, and cyclic voltammetry). Prior to their synthesis, trimer structures were modeled by DFT calculations facilitating a further understanding of the systems' electronic and geometric structure. Polymers were titrated with acid and base to take advantage of their amphiprotic imidazole moiety and their optical response monitored with ultraviolet–visible spectroscopy. Finally, pristine polymer thin‐films were treated with acid and base to evaluate (de)protonation's effect on system electronics, but thin‐film degradation was encountered. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 60–69     

Medium band gap conjugated polymers from thienoacene derivatives and pentacyclic aromatic lactam as promising alternatives of poly(3‐hexylthiophene) in photovoltaic application

Two alternating medium band gap conjugated polymers (PBDT‐TPTI and PDTBDT‐TPTI) derived from 4,8‐bis(4,5‐dioctylthien‐2‐yl)benzo[1,2‐b:4,5‐b′]dithiophene (BDT‐T) or 5,10‐bis(4,5‐didecylthien‐2‐yl)dithieno[2,3‐d:2′,3′‐d′]benzo[1,2‐b:4,5‐b′]dithiophene (DTBDT‐T) with pentacyclic aromatic lactam of N,N‐didodecylthieno[2′,3′:5,6]pyrido[3,4‐g]thieno[3,2‐c]‐iso‐quinoline‐5,11‐dione (TPTI), are synthesized and characterized. The comparative investigation of the photostabilities of the copolymers revealed that the PDTBDT‐TPTI film exhibited the comparable photostability in relative to P3HT. Meanwhile, the inverted photovoltaic cells (i‐PVCs) from the blend films of PBDT‐TPTI and/or PDTBDT‐TPTI with PC₇₁BM, in which poly[(9,9‐bis(3′‐(N,N‐dimethylamino)propyl)‐2,7‐fluorene)‐alt‐2,7‐(9,9‐dioctylfluorene)] were used as cathode modifying interlayer, presented higher power conversion efficiencies (PCEs) of 5.98% and 6.05% with photocurrent response ranging from 300 nm to 650 nm in contrast with the PCEs of 4.48% for the optimal inverted PVCs from P3HT/PC₇₁BM under AM 1.5 G 100 mW/cm². The PCEs of the i‐PVCs from PBDT‐TPTI and PDTBDT‐TPTI were improved to 7.58% and 6.91% in contrast to that of 0.02% for the P3HT‐based i‐PVCs, and the photocurrent responses of the devices were extended to 300–792 nm, when the ITIC was used as electron acceptor materials. The results indicate that the PBDT‐TPTI and PDTBDT‐TPTI can be used as the promising alternatives of notable P3HT in the photovoltaic application. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 85–95     

Reduced‐bandgap triphenylamine‐alt‐benzo[1,2‐b:4,5‐b′]dithiophene copolymers pending benzothiadiazole or diketopyrrolopyrrole units for efficient polymer solar cells

Two new side‐chain donor–acceptor (D‐A)‐based triphenylamine‐alt‐benzo[1,2‐b:4,5‐b′]dithiophene (TPA‐alt‐BDT) copolymers ( P1 and P2 ) with pendant benzothiadiazole (BT)/diketopyrrolopyrrole (DPP) in TPA unit were synthesized by Stille coupling polymerization. Their thermal, photophysical, electrochemical, blend film morphology and photovoltaic properties were investigated. Efficient bulk heterojunction polymer solar cells (PSCs) were obtained by solution process using both copolymers as donor materials and PC₇₁BM as acceptor. The maximum power conversion efficiency (PCE) of 3.17% with a highest open‐circuit voltage (V_oc) of 0.86V was observed in the P1 ‐based PSCs, while the maximum short‐circuit current (J_sc) of 10.77 mA cm^?2 was exhibited in the P2 ‐based PSCs under the illumination of AM 1.5, 100 mW cm^?2. The alternating binary donor units and pending acceptor groups played a significant role in tuning photovoltaic properties for this class of the side‐chain D–A‐based copolymers. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4103–4110     

Rigid Nonfullerene Acceptors Based on Triptycene–Perylene Dye for Organic Solar Cells

Three kinds of nonconjugated rigid perylene bisimide (PBI) derivatives based on a triptycene core were designed, synthesized and characterized. The unique three‐dimensional (3D) conformation of triptycene could enable formation of polymer with the favorable morphology for organic polymer solar cells (PSCs) by relieving the self‐aggregation of rigid PBI units. The low‐lying LUMO energy levels of these compounds demonstrated that they are very suitable for use as acceptors in organic solar cells. A higher power conversion efficiency (PCE) of 6.15 % was obtained for the blend film using the compound with two PBI units ( T‐2 ) as the acceptor and commercial poly[[4,8‐bis[5‐(2‐ethylhexyl)thiophene‐2‐yl]benzo[1,2‐b :4,5‐b ′]dithiophene‐2,6‐diyl][3‐fluoro‐2‐[(2‐ethylhexyl)‐carbonyl]thieno[3,4‐b ]thiophenediyl]] (PCE‐10) as the electron donor.     

Sb2Se3‐Sensitized Inorganic–Organic Heterojunction Solar Cells Fabricated Using a Single‐Source Precursor

The photovoltaic performance of Sb₂Se₃‐sensitized heterojunction solar cells, which were fabricated by a simple deposition of Sb₂Se₃ on mesoporous TiO₂ by an approach that features multiple cycles of spin coating with a single‐source precursor solution and thermal decomposition, is reported. Poly[2,6‐(4,4‐bis(2‐ethylhexyl)‐4H‐cyclopenta[2,1‐b;3,4‐b′]dithiophene)‐alt‐4,7(2,1,3‐benzothioadiazole)] was used as the hole‐transporting material. The most efficient cell exhibited a short‐circuit current density of 22.3 mA cm^?2, an open‐circuit voltage of 304.5 mV, and a fill factor of 47.2 %, yielding a power conversion efficiency of 3.21 % under standard test conditions (irradiation of 1000 W m^?2, air mass=1.5 G). The results of this study imply that the developed approach has a high potential as a simple and effective route for the fabrication of efficient and inexpensive solar cells.     

Modification of Hole Transport Layers for Fabricating High Performance Non‐fullerene Polymer Solar Cells

Interfacial engineering is expected to be a feasible strategy to improve the charge transport properties of the hole transport layer (HTL), which is of crucial importance to boost the device performance of organic solar cells (OSCs). In this study, two types of alcohol soluble materials, 2,3,5,6‐tetrafluoro‐7,7,8,8‐tetracyanoquinodimethane (F₄‐TCNQ) and di‐tetrabutylammoniumcis–bis(isothiocyanato)bis (2,2’‐bipyridyl‐4,4’‐dicarboxylato) ruthenium(II) (N719) dye were selected as the dopant for HTL. The doping of F₄‐TCNQ and N719 dye in poly (ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) with and without integrating a graphene quantum‐dots (G‐QDs) layer has been explored in 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]thio‐phenediyl:(2,2′‐((2Z,2′Z)‐(((4,4,9, 9‐tetrakis(4‐hexylphenyl)‐4,9‐dihydro‐s‐indaceno[1,2‐b:5,6‐b′]dithiophene‐2,7‐diyl)bis(4‐((2‐ethylhexyl)oxy)thiophene‐5,2‐diyl))bis(methanylylidene))bis(5,6‐difluoro‐3‐oxo‐2,3‐dihydro‐1H‐indene‐2,1‐diylidene))dimalononitrile (PTB7‐Th:IEICO‐4F) OSCs. The power conversion efficiency of the non‐fullerene OSCs has been increased to 10.12% from 8.84%. The influence of HTL modification on the nano‐morphological structures and photophysical properties is analyzed based on the comparative studies performed on the control and modified devices. The use of chemical doping and bilayer strategy optimizes the energy level alignment, nanomorphology, hole mobility, and work‐function of HTL, leading to considerable reduction of the leakage current and recombination losses. Our work demonstrates that the doping of HTL and the incorporation of G‐QDs layer to constitute a bilayer HTL is an promising strategy to fabricate high performance non‐fullerene polymer solar cells     

Synthesis and characterization of cyclopentadithiophene‐based low bandgap copolymers containing electron‐deficient benzoselenadiazole derivatives for photovoltaic devices

We have synthesized two cyclopentadithiophene (CDT)‐based low bandgap copolymers, poly[(4,4‐bis(2‐ethyl‐hexyl)‐4H‐cyclopenta[2,1‐b:3,4‐b′]dithiophene‐2,6‐diyl)‐alt‐(benzo[c][1,2,5]selenadiazole‐4,7‐diyl)] (PCBSe) and poly[(4,4‐bis(2‐ethyl‐hexyl)‐4H‐cyclopenta[2,1‐b:3,4‐b′]dithiophene‐2,6‐diyl)‐alt‐(4,7‐dithiophen‐2‐yl‐benzo[c][1,2,5]selenadiazole‐5,5′‐diyl)] (PCT2BSe), for use in photovoltaic applications. Through the internal charge transfer interaction between the electron‐donating CDT unit and the electron‐accepting benzoselenadiazole, we realized exceedingly low bandgap polymers with bandgaps of 1.37–1.46 eV. The UV–vis absorption maxima of PCT2BSe were subjected to larger hypsochromic shifts than those of PCBSe, because of the distorted electron donor–acceptor (D–A) structures of the PCT2BSe backbone. These results were supported by the calculations of the D–A complex using the ab initio Hartree‐Fock method with a split‐valence 6‐31G* basis set. However, PCT2BSe exhibited a better molar absorption coefficient in the visible region, which can lead to more efficient absorption of sunlight. As a result, PCT2BSe blended with [6,6]‐phenyl‐C₆₁‐butyric acid methyl ester (PC₆₁BM) exhibited a better photovoltaic performance than PCBSe because of the larger spectral overlap integral with respect to the solar spectrum. Furthermore, when the polymers were blended with PC₇₁BM, PCT2BSe showed the best performance, with an open circuit voltage of 0.55 V, a short‐circuit current of 6.63 mA/cm², and a power conversion efficiency of 1.34% under air mass 1.5 global illumination conditions. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1423–1432, 2010     

Synthesis of Amphiphilic RuII Heteroleptic Complexes Based on Benzo[1,2‐b:4,5‐b′]dithiophene: Relevance of the Half‐Sandwich Complex Intermediate and Solvent Compatibility

The detailed synthesis and characterization of four ruthenium(II) complexes [RuLL′(NCS)₂] is reported, in which L represents a 2,2′‐bipyridine ligand functionalized at the 4,4′ positions with benzo[1,2‐b:4,5‐b′]dithiophene derivatives (BDT) and L′ is 2,2′‐bipyridine‐4,4′‐dicarboxylic acid unit (dcbpy) (NCS=isothiocyanate). The reaction conditions were adapted and optimized for the preparation of these amphiphilic complexes with a strong lipophilic character. The photovoltaic performances of these complexes were tested in TiO₂ dye‐sensitized solar cell (DSSC) achieving efficiencies in the range of 3–4.5 % under simulated one sun illumination (AM1.5G).     

CuSbS2‐Sensitized Inorganic–Organic Heterojunction Solar Cells Fabricated Using a Metal–Thiourea Complex Solution

The device performance of sensitizer‐architecture solar cells based on a CuSbS₂ light sensitizer is presented. The device consists of F‐doped SnO₂ substrate/TiO₂ blocking layer/mesoporous TiO₂/CuSbS₂/hole‐transporting material/Au electrode. The CuSbS₂ was deposited by repeated cycles of spin coating of a Cu‐Sb‐thiourea complex solution and thermal decomposition, followed by annealing in Ar at 500 °C. Poly(2,6‐(4,4‐bis‐(2‐ethylhexyl)‐4H‐cyclopenta[2,1‐b;3,4‐b′]dithiophene)‐alt‐4,7(2,1,3‐benzothiadiazole)) (PCPDTBT) was used as the hole‐transporting material. The best‐performing cell exhibited a 3.1 % device efficiency, with a short‐circuit current density of 21.5 mA cm^?2, an open‐circuit voltage of 304 mV, and a fill factor of 46.8 %.     

Synthesis and characterization of highly conjugated side‐group‐substituted benzo[1,2‐b:4,5‐b′]dithiophene‐based copolymer for use in organic solar cells

A new donor–acceptor (D–A) conjugated copolymer based on benzo[1,2‐b:4,5‐b′]dithiophene (BDT) and thieno[3,4‐c]pyrrole‐4,6‐dione (TPD) was synthesized via a Stille cross‐coupling reaction. A highly conjugated thiophene‐based side group, tris(thienylenevinylene) (TTV), was incorporated into each BDT unit to generate the two‐dimensional D–A copolymer (PBDT‐TTV). An alkoxy‐substituted BDT‐based TPD copolymer (PBDT‐OR) was synthesized using the same polymerization method for comparison. PBDT‐TTV thin films produced two distinct absorption peaks. The shorter wavelength absorption (458 nm) was attributed to the BDT units containing the TTV group, and the longer wavelength band (567–616 nm) was attributed to intramolecular charge transfer between the BDT donor and the TPD acceptor. The highest occupied molecular orbital energy levels of PBDT‐OR and PBDT‐TTV were calculated to be −5.53 and −5.61 eV, respectively. PBDT‐TTV thin films harvested a broad solar spectrum covering the range 300–700 nm. A comparison with the PBDT‐OR films revealed stronger interchain π–π interactions in the PBDT‐TTV films and, thus, a higher hole mobility. A polymer solar cell device prepared using PBDT‐TTV as the active layer was found to exhibit a higher power conversion efficiency than a device prepared using PBDT‐OR under AM 1.5 G (100 mW/cm²) conditions. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 653–660     

Recent Progress in All‐Polymer Solar Cells Based on Wide‐Bandgap p‐Type Polymers

All‐polymer solar cells (all‐PSCs), with the photoactive layer exclusively composed of polymers as both donor and acceptor, have attracted growing attention due to their unique merits in optical, thermal and mechanical durability. Through the combined strategies in materials design and device engineering, recently the power conversion efficiencies of single‐junction all‐PSCs have been boosted up to 11 %. This review focuses on the recent progress of all‐PSCs comprising of wide band‐gap p‐type polymers, especially those based on the units of thieno[3,4‐c]pyrrole‐4,6(5H)‐dione], fluorinated benzotriazole, benzo[1,2‐c:4,5‐c′]dithiophene‐4,8‐dione, and pyrrolo[3,4‐f]benzotriazole‐5,7(6H)‐dione. Meantime, several categories of n‐type polymers used to match with these polymer donors are also reviewed. Finally, a brief summary of the strategies of molecular design and morphology optimization is given, and strategies toward further improving performance of all‐PSCs are outlined.     

Donor–acceptor‐structured naphtodithiophene‐based copolymers for organic thin‐film transistors

New donor–acceptor (D‐A) polymers, poly(4,5‐bis(2‐octyldodecyloxy)naphto[2,1‐b:3,4‐b']dithiophenebenzo[c][1,2,5]thiadiazole) (PNDT‐B) and poly(4,5‐bis(2‐octyldodecyloxy)naphto [2,1‐b:3,4‐b′]dithiophene‐4,7‐di(thiophen‐2‐yl)benzo[c][1,2,5]thiadiazole) (PNDT‐TBT), with the extended π‐electron delocalization of naphtho[2,1‐b:3,4‐b']dithiophene, were successfully synthesized by Suzuki and Stille coupling reactions. The structure and physical properties of polymers were characterized by DFT calculation, UV–vis absorption, cyclovoltammetry, TGA and DSC analyses. X‐ray diffraction studies indicated a relatively highly ordered intermolecular structure in PNDT‐TBT after annealing. This high degree of molecular order resulted from the crystallinity and increasing planarity, provided by the thiophene linker groups and the interdigitation of the long alkoxy side chains. The new D‐A polymer, PNDT‐TBT, exhibited a p‐type carrier mobility of 0.028 cm²/Vs and an on/off ratio of 5.9 × 10³. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 525–531