Degenerately Doped Semi-Crystalline Polymers for High Performance Thermoelectrics

Thermoelectric (TE) energy conversion in conjugated polymers is considered a promising approach for low-energy harvesting and self-powered temperature sensing. To enhance the TE performance, it is necessary to understand the relationship between the Seebeck coefficient (α) and electrical conductivity (σ). Typical doped polymers exhibit α–σ relationship that is distinct from that of inorganic materials due to their large structural and energetic disorder, which prevents them from achieving the maximum TE power factor (PF = α²σ). Here, an ideal α–σ relationship in the Kang–Snyder model following a transport parameter s  = 1 is demonstrated with two degenerately doped semi-crystalline polymers, poly[(4,4′-(bis(hexyldecylsulfanyl)methylene)cyclopenta[2,1-b:3,4-b′]dithiophene)-alt-(benzo[c][1,2,5]thiadiazole)] (PCPDTSBT) and poly[(2,5-bis(2-hexyldecyloxy)phenylene)-alt-(5,6-difluoro-4,7-di(thiophen-2-yl)benzo[c][1,2,5]thiadiazole)] (PPDT2FBT) using a sequential doping method. The results allow the realization of the PFs reaching theoretic maxima (i.e., 112.01  µ W m⁻¹ K⁻² for PPDT2FBT and 49.80  µ W m⁻¹ K⁻² for PCPDTSBT) and close to metallic behavior in heavily doped films. Additionally, it is shown that the PF maxima appear when the doping state switches from non-degenerate to degenerate. Strategies towards an optimal α–σ relationship enable optimization of the PF and provide an understanding of the charge transport of doped polymers.     

Infrared proximity sensor using organic light-emitting diode with quantum dots converter

An efficient visible-to-infrared conversion film is made by blending CdTe quantum dots (CdTe QDs) of 12 nm diameter in a polyvinylpyrrolidone 360 (PVP 360) polymer matrix cast by water solution. The solid-state photoluminescence quantum efficiency exceeds 10% with emission peak at 810 nm. Strong 810 emission is obtained by combining the quantum dot film and a green polyfluorene light-emitting diode. Color filter is used to remove residual light below 780 nm to make it entirely invisible. Infrared photo-detector is made by blending poly[5-(5-(2,5-bis(decyloxy)-4-methylphenyl)thiophen-2-yl)-2,3-bis(4-(2-ethylhexyloxy)phenyl)-7-(5-methylthiophen-2-yl)thieno[3,4-b]pyrazine] (PBDOTTP) with band-gap 1.2 eV and (6,6)-phenyl-C61-butyric acid methyl ester (PCBM). The pixel contains one PD surrounded by four PLED on its four sides. The active areas of the five devices are all 1 cm by 1 cm and they are on the same plane. Infrared proximity sensor with photo-current over 300 nA at 10 cm object distance is achieved by detecting the reflected infrared signal.     

Synthesis and characterizations of poly(3,6-thienophenanthrene) and poly(2,7-thienophenanthrene) and their applications in polymer light-emitting devices and solar cells

Here we report the synthesis of two novel phenylene-based polymers-poly(3,6-thienophenanthrene) (PTP36) and poly(2,7-thienophenanthrene) (PTP27) via base-free Suzuki–Miyaura reaction. The structure and electroluminescent properties of the meta-linked PTP36 and para-linked PTP27 are fully characterized. The obtained polymers were found to be liquid-crystalline, with broad band gap of 2.72 eV and 2.49 eV, respectively, which are much smaller than those of corresponding polyphenanthrenes. On the basis of PTP36 and PTP27, copolymers of 2,7-thienophenanthrene and 3,6-thienophenanthrene with 5,6-bis(octyloxy)-4,7-di(thiophen-2-yl)benzothiadiazole (DBT), namely PTP36-DBT and PTP27-DBT were prepared and be investigated as a potential donor material for polymer solar cells. The preliminary data show that the maximal power conversion efficiencies (PCEs) of the PTP27-DBT- and PTP36-DBT-based polymer solar cells are 3.5% and 0.9%, respectively.     

Silaindacenodithiophene‐Based Low Band Gap Polymers – The Effect of Fluorine Substitution on Device Performances and Film Morphologies

Silaindacenodithiophene is copolymerized with benzo[c][1,2,5]thiadiazole ( BT ) and 4,7‐di(thiophen‐2‐yl)benzo[c][1,2,5]thiadiazole ( DTBT ), respectively their fluorinated counter parts 5,6‐difluorobenzo[c][1,2,5]thiadiazole ( 2FBT ) and 5,6‐difluoro‐4,7‐di(thiophen‐2‐yl) benzo[c][1,2,5]thiadiazole ( 2FDTBT ). The influence of the thienyl spacers and fluorine atoms on molecular packing and active layer morphology is investigated with regard to device performances. bulk heterojunction (BHJ) solar cells based on silaindacenodithiophene donor‐acceptor polymers achieved PCE's of 4.5% and hole mobilities of as high as 0.28 cm²/(V s) are achieved in an organic field‐effect transistor (OFET).     

Asymmetric medium bandgap copolymers and narrow bandgap small-molecule acceptor with over 7% efficiency

To further investigate non-fullerene polymer solar cells based-thieno[2,3-f]benzofuran (TBF) polymers, we designed and synthesized two medium bandgap TBF-based polymers, namely TBF-BDD and TBF-BT, containing alkoxyphenyl substituted TBF electron-donor unit, 1,3-bis(thiophen-2-yl)-5,7-bis(2-ethylhexyl)benzo-[1,2-c:4,5-c′]dithiophene-4,8-dione (BDD) and 4,7-di(thiophen-2-yl)-5,6-dioctyloxybenzo[c][1,2,5]thiadiazole (BT) electron-acceptor segment, respectively. When blended with ITIC (a n-type small molecule acceptor), two polymer:ITIC blends possess better complementary absorption than the absorption with PC₇₁BM. The properties, including charge mobilities, and morphologies have been intensively investigated. The polymer solar cells based on TBF-BDD:ITIC and TBF-BT:ITIC (1:1,w/w) exhibited promising power conversion efficiencies (PCEs) of 7.13% and 7.03%, respectively, under the illumination of AM 1.5 G, 100 mW/cm², which are higher in comparison with fullerene-based devices. Up to now, these PCEs are the highest among TBF-based polymer photovoltaic devices.     

Efficient semitransparent organic solar cells with good color perception and good color rendering by blade coating

This paper proposes high efficiency semitransparent organic solar cells (OSCs) with good color perception and good color rendering using blade coating technique. We investigate four different polymer blends and first fabricate small area devices with active area of 0.04 cm², followed by large area devices with active area of 10.8 cm². Two of the polymer blends, 2,6-Bis(trimethyltin)-4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b']dithiophene:6,6-phenyl C71-butyric acid methyl ester (PBDTTT-CT:PC₇₁BM) and poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b;4,5-b′] dithiophene-2,6-diyl-alt-(4-(2-ethylhexyl)-3-fluorothieno[3,4-b]thiophene-)-2-carboxylate-2-6-diyl)]:PC₇₁BM (PBDTTT-EFT:PC₇₁BM) show promising results. For small area devices, semitransparent PBDTTT-CT:PC₇₁BM and semitransparent PBDTTT-EFT:PC₇₁BM achieve a power conversion efficiency (PCE) of 5.2% (opaque PCE = 7.5%) and 5.6% (opaque PCE = 9.4%) respectively. For large area devices, they are found to produce a PCE of 3.8% (opaque PCE = 4.2%) and 5.3% (opaque PCE = 5.9%) respectively. Based on the CIE 1931 chromaticity diagram, semitransparent PBDTTT-CT:PC₇₁BM and semitransparent PBDTTT-EFT:PC₇₁BM are located very close to the standard illuminant D65, indicating good color perception. As for color rendering, they demonstrate high color rendering index (CRI) of 95.4 and 87.1 respectively. These combined high performances indicate high-quality transmitted light, which is suitable for window application.     

Visibly transparent conjugated polymers based on non-alternant cyclopenta-fused emeraldicene for polymer solar cells

In this study, we synthesized two emeraldicene (EMD)-based conjugated polymers, PBTEMD and PFEMD, through polymerization of 4,7-di(thien-2-yl)benzo[c][1,2,5]thiadiazole and 9,9-bis(2-ethylhexyl)-9H-fluorene, respectively. We then blended these EMD-derived polymers (as electron-donating materials) with [6,6]-phenyl-C₇₁-butyric acid methyl ester (PC₇₁BM) in the active layers of polymer solar cells (PSCs) and investigate their optoelectronic properties and related photovoltaic performance. To best of our knowledge, this study is the first to use EMD derivatives for PSC applications. We compared the molecular structures, absorption behavior, energy levels, thermal properties, and thermal stability of these two polymers to determine their suitability for use in PSCs. The main absorption of PFEMD was in the near-IR spectrum (600–800 nm). We observed a transparency of greater than 80% for the blend film of PFEMD having a thickness of 95 nm; the constructed device exhibited a power conversion efficiency (PCE) of 2.5% and the transparent PFEMD:PC₆₁BM-derived device exhibited a PCE of 1.2% under AM 1.5 G irradiation (100 mW cm⁻²). We observed a significant improvement in thermal stability for the device incorporating the additive crosslinker TBT-N₃; it retained approximately 60% of its initial PCE after accelerated heating (150 °C) for 18 h. In contrast, the PCE of the corresponding normal device decayed to 0.01% of its initial value.     

Donor-acceptor polymers based on 5,6-difluoro-benzo[1,2,5]thiadiazole for high performance solar cells

Two donor-acceptor polymers P8 and P9 based on 5,6-difluoro-benzo[1,2,5]thiadiazole unit have been prepared and applied as the donor materials in polymer solar cells. Due to the slight difference between electronic structures of thiophene and selenophene, P8 and P9 show similar absorption spectra and similar frontier energy levels. However, the pristine P8:PC₇₁BM and P9:PC₇₁BM blend films display distinct morphologies as revealed by AFM measurement. After the addition of DIO, both blend films feature a nanoscale interconnected-network structure, which leads to the enhancement in solar cells performance with PCE up to 6.73% and 6.84% for P8 and P9, respectively. Alternating current impedance spectrometry measurements revealed that high surface roughness could improve the PCE of P8-based PSCs, while in P9-based PSCs DIO can enhance hole and electron mobilities of the active layer.     

Influence of the Electron Deficient Co‐Monomer on the Optoelectronic Properties and Photovoltaic Performance of Dithienogermole‐based Co‐Polymers

A series of donor–acceptor (D–A) conjugated polymers utilizing 4,4‐bis(2‐ethylhexyl)‐4H‐germolo[3,2‐b:4,5‐b′]dithiophene ( DTG ) as the electron rich unit and three electron withdrawing units of varying strength, namely 2‐octyl‐2H‐benzo[d][1,2,3]triazole ( BTz ), 5,6‐difluorobenzo[c][1,2,5]thiadiazole ( DFBT ) and [1,2,5]thiadiazolo[3,4‐c]pyridine ( PT ) are reported. It is demonstrated how the choice of the acceptor unit ( BTz , DFBT , PT ) influences the relative positions of the energy levels, the intramolecular transition energy (ICT), the optical band gap (E_g^opt), and the structural conformation of the DTG ‐based co‐polymers. Moreover, the photovoltaic performance of poly[(4,4‐bis(2‐ethylhexyl)‐4H‐germolo[3,2‐b:4,5‐b′]dithiophen‐2‐yl)‐([1,2,5]thiadiazolo[3,4‐c]pyridine)] ( PDTG‐PT ), poly[(4,4‐bis(2‐ethylhexyl)‐4H‐germolo[3,2‐b:4,5‐b′]dithiophen‐2‐yl)‐(2‐octyl‐2H‐benzo[d][1,2,3]triazole)] ( PDTG‐BTz ), and poly[(4,4‐bis(2‐ethylhexyl)‐4H‐germolo[3,2‐b:4,5‐b′]dithiophen‐2‐yl)‐(5,6‐difluorobenzo[c][1,2,5]thiadiazole)] ( PDTG‐DFBT ) is studied in blends with [6,6]‐phenyl‐C₇₀‐butyric acid methyl ester ( PC₇₀BM ). The highest power conversion efficiency (PCE) is obtained by PDTG‐PT (5.2%) in normal architecture. The PCE of PDTG‐PT is further improved to 6.6% when the device architecture is modified from normal to inverted. Therefore, PDTG‐PT is an ideal candidate for application in tandem solar cells configuration due to its high efficiency at very low band gaps (E_g^opt = 1.32 eV). Finally, the 6.6% PCE is the highest reported for all the co‐polymers containing bridged bithiophenes with 5‐member fused rings in the central core and possessing an E_g^opt below 1.4 eV.     

Donor–acceptor copolymers based on benzo[1,2-b:4,5-b′]dithiophene and pyrene-fused phenazine for high-performance polymer solar cells

Two novel donor–acceptor (D–A)-type conjugated polymers of PTTPPz-BDT and PTTPPz-BDTT were successfully synthesized by Stille coupling polymerization, in which 7,8-dialkoxy benzo[1,2-b:4,5-b′]dithiophene (BDT) and 7,8-bithienyl benzo[1,2-b:4,5-b′]dithiophene (BDTT) were used as donor units, thiophene and pyrene-fused phenazine (PPz) were employed as π-bridges and acceptor units, respectively. High carrier mobilities, broad absorption spectra, narrow optical band gaps, and low HOMO energy levels were observed for both polymers. Furthermore, high-efficiency photovoltaic performance with power conversion efficiency (PCE) over 4.25% was exhibited in their polymer solar cells (PSCs) using [6,6]-phenyl-C₇₁-butyric-acid-methyl-ester (PC₇₁BM) as acceptor. The maximum PCE of 4.86% with short-circuit current density of 11.10 mA cm⁻² and fill factor of 62.5% was obtained in the PTTPPz-BDTT based cell. These results indicate that incorporating large planar PPz moiety into D–A-type copolymer is an efficient approach to improve photovoltaic performance for PSCs.     

Synthesis and photovoltaic studies on novel fluorene based cross-conjugated donor-acceptor type polymers

Direct arylation polymerization (DAP) is emerging as a promising green, cheap, simple, and efficient environment friendly method for synthesizing conjugated polymers without involving any organometallic reagent. We report fluorene based novel cross-conjugated alternate and random copolymers for polymer solar cells (PSCs), which were synthesized by DAP and/or Yamamoto polymerization under appropriate reaction conditions to obtain high molecular weight. These cross-conjugated polymers possess absorption maxima in the range of 490–520 nm and have narrow band gap (1.7–2.05 eV) which is suitable for bulk heterojuntion (BHJ) type organic solar cells. Among the synthesized polymers, the highest number average molecular weight (M_n) i.e. 43.1 kg mol⁻¹ was obtained for polymer P2b (poly((9H-fluoren-9-ylidene)methylene)bis((2-ethylhexyl)sulfane)-alt-4,7-di(thiophen-2-yl)benzo[c][1,2,5]thiadiazole)), and so good polymeric films were formed for P2b. Thus, BHJ films were prepared for P2b for device performance studies and the morphology of these films was studied by atomic force microscopy (AFM). Polymer P2b was blended with the fullerene derivative [6,6]-phenyl C₇₁ butyric acid methyl ester (PC₇₁BM) in different ratios and under the illumination of solar simulator with Air Mass global (AM 1.5G) irradiated at 100 mW cm⁻². Power conversion efficiency (PCE) of 1.4% has been achieved for BHJs in ratio of 1:2 of P2b: PC₇₁BM in simply processed devices. This result indicates that cross-conjugated polymers can be tapped as potential donors for BHJs as the PCE obtained is the highest among this type of cross-conjugated polymers.     

[1,2,5]Thiadiazolo[3,4-f]benzotriazole based narrow band gap conjugated polymers with photocurrent response up to 1.1 μm

Three novel donor–acceptor type of narrow band gap conjugated copolymers were synthesized through a palladium-catalyzed Stille copolymerization based on [1,2,5]thiadiazolo[3,4-f]benzotriazole (TBZ) derivatives as acceptor and 4,8-di(2,3-didecylthiophen-5-yl)-benzo[1,2-b:4,5-b′]dithiophene (BDT) as donor. All resulted copolymers exhibited absorbance up to near-infrared region along with relatively narrow band gap in the range of 0.96–1.10 eV. Cyclic voltammetry measurements illustrated that the highest occupied molecular orbital energy levels of copolymers lay in the range of −5.04 to −5.13 eV, and lowest unoccupied molecular orbital (LUMO) energy levels were in the range of −4.03 to −4.16 eV. Photovoltaic performances were evaluated based on the resulted copolymers as donor and [6,6]-phenyl-C₆₀ butyric acid methyl ester (PC₆₁BM) as acceptor with optimized weight ratio of 1:2. All devices displayed comparatively low power conversion efficiencies in the range of 0.1–0.4% due to the low-lying LUMO energy levels. Broad photocurrent response up to near infrared region of 1.1 μm was realized for copolymer P2 that containing thiophene unit as the bridge between BDT and TBZ moieties, indicating that it can be potentially applied for near infrared photodetectors.     

Morphology optimization of organic solar cells enabled by interface engineering of zinc oxide layer with a conjugated organic material

A diphenylphosphine-oxide-based conjugated organic molecule, ((1,3,5-triazine-2,4,6-triyl)tris(benzene-3,1-diyl))tris(diphenylphosphine oxide) (PO-T2T), was doped into ZnO to improve the characteristics of the electron transport layer (ETL) in inverted organic solar cells (OSCs). A series of characterization techniques were carried out to demonstrate the function of PO-T2T in film aspect, including transmittance, atomic force microscopy (AFM), transmission electron microscopy (TEM), water contact angle and grazing incidence wide angle X-ray scattering (GIWAXS). Light dependent, space-charge-limited current, exciton dissociation possibility were aimed to explore the influence of PO-T2T for internal carrier behaviors based on PTB7-Th: PC₇₁BM system. It's found that the PO-T2T doped ETLs played a role in morphology optimization of ETL and undermined the trap-assistant recombination through filling the defects ZnO itself had, simultaneously. Besides, the electron mobility was also improved. With the optimized functionalities, the OSCs' efficiency based on fullerene system Poly[4,8- bis(5-(2-Ethylhexyl)thiophen-2-yl) benzo [1,2-b:4,5-b′] dithiophene-co-3-fluorothieno [3,4-b] thiophene-2-carboxylate] (PTB7-Th): [6,6]-Phenyl C71 butyric acid methyl ester (PC₇₁BM) was improved from 9.03% to 9.84%. Finally, when this strategy was applied into another hot-topic system, poly((2,6-(4,8-bis(5-(2-ethylhexyl-3- fluoro)thiophen-2-yl)-benzo[1,2-b:4,5-b′]dithiophene))-alt-(5,5- (1′,3′-di-2-thienyl)-5′,7′-bis(2-ethylhexyl)benzo[1′,2′-c:4′,5′-c′] dithiophene-4,8-dione)) (PBDB-TF):2,2′-((2Z,2′Z)-((12,13-bis(2- ethylhexyl)-3,9-diundecyl-12,13-dihydro-[1,2,5]thiadiazolo[3,4-e] thieno[2,″3″:4′,5′]thieno[2′,3′:4,5]pyrrolo[3,2-g]thieno[2′,3′:4,5] thieno[3,2-b]indole-2,10-diyl)bis(methanylylidene))bis(5,6-difluoro-3-oxo-2,3-dihydro-1H-indene-2,1-diylidene))dimalononitrile (Y6), a high PCE of 16.34% was obtained. These results demonstrated that the PO-T2T had a positive role in OSC performance improvement.     

Poly(thieno[3,4-b][1,4]dioxine) and poly([1,4]dioxino[2,3-c]pyrrole) derivatives: p- and n-dopable redox-active electrode materials for solid state supercapacitor applications

We report the synthesis and supercapacitive properties of novel poly(2,3,4a,9a-tetrahydro[1,4]dioxino[2,3-b]thieno[3,4-e][1,4]dioxine) (pTDTD) and poly(7-butyl-3,4a,7,9a-tetrahydro-2H-[1,4]dioxino[2′,3′:5,6][1,4]dioxino[2,3-c]pyrrole) (pTDDP) as redox-active electrode materials for supercapacitor applications. At first, new thiophene and pyrrole monomers containing of fused two 1,4-dioxane rings were successfully synthesized and their conducting polymers were prepared electrochemically on a stainless steel (SS) electrode. Symmetric and asymmetric solid state pseudocapacitor devices were fabricated in order to evaluate supercapacitive performances of newly designed pTDTD and pTDDP. The SS electrodes modified with pTDTD and pTDDP were used as an anode material against pEDOT coated SS cathode in asymmetric devices and as both anode and cathode material in symmetric devices. Capacitive behaviors and performances of the devices were tested by cyclic voltammetry (CV), galvanostatic charge/discharge (GCD) and electrochemical impedance spectroscopy (EIS) techniques. In symmetric devices, pTDTD provided a specific capacitance of 260 F/g and specific energy of 288 W h/kg, while the pTDDP was found to be not a suitable redox-active electrode material for pseudocapacitor applications.     

Synthesis and photovoltaic properties of D-A copolymers based on alkylthio-thiophene or alkylthio-selenophene-BDT donor unit and DPP acceptor unit

Two new 2D-conjugated D-A copolymers, PBDTT-S-DPP and PBDTSe-S-DPP, based on benzodithiophene (BDT) donor unit with alkylthio-thiophene or alkylthio-selenophene conjugated side chains and 2,5-bis(2-butyloctyl)-3,6-di(thiophen-2-yl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione) (DPP) acceptor unit, were synthesized for the application as donor materials in polymer solar cells (PSCs). The two polymers were characterized by absorption spectroscopy, cyclic voltammetry, thermogravimetric analysis, theoretical calculation with density functional theory, X-ray diffraction and photovoltaic measurements. The results show that the alkylthio-thiophene/selenophene side groups on BDT unit and intramolecular hydrogen bonding interaction in DPP acceptor unit play important roles in affecting the absorption, HOMO energy levels, molecular planarity and the crystallinity of the polymers. The PSCs based on PBDTT-S-DPP or PBDTSe-S-DPP as donor and PC₇₁BM as acceptor demonstrate power conversion efficiency (PCE) of 5.62% and 5.01%, with relatively higher V_oc of 0.79 V and 0.76 V, respectively.     

Side chain engineering on D18 polymers yields 18.74％ power conversion efficiency

Donor-acceptor (D-A) conjugated copolymers contain-ing fused-ring acceptor units demonstrate outstanding per-formance in organic solar cells (OSCs)[1-13].We have in-vented highly efficient D-A copolymer donors D18 and D18-CI by using a fused-ring acceptor unit,dithieno[3',2':3,4;2",3":5,6]benzo[1,2-c][1,2,5]thiadiazole (DTBT)[1,2].OSCs with D18 or D18-CI gave power conversion efficiencies(PCEs) of 18.56％ and 18.69％,respectively[3,4].Side chain engineering is an effective approach to improve the per-formance of conjugated polymers in optoelectronic devi-ces[14-16].The alkyl side chains not only determine polymers' solubility,but also influence their crystallinity and mobility.In this work,we develop two efficient donors D18-B and D18-CI-B via side chain engineering on D18 polymers (Fig.1(a)).These donors offer PCEs up to 18.74％ (certified 18.2％) in tern-ary OSCs.     

Thermo-cleavable poly(fluorene-benzothiadiazole) to enable solution deposition of multi-layer organic light emitting diodes

The design of solution processable multi-layer organic light emitting diodes (OLEDs) is often hampered by the choice of solvents. To avoid the dissolution of the emission layer upon the subsequent deposition of further functional layers, we synthesize and investigate thermo-cleavage in poly[2,7-(3-(9-methyl-9H-fluorene-9-yl)propyl (2-methylhexane-2-yl) carbonate)-alt-4,7-(benzo[c][1,2,5]thiadiazole)] (c-F8BT). Employed in OLEDs, the non-cleaved polymer yields about the same current efficiency as state-of-the-art F8BT. During pyrolysis at 200 °C, the polymer releases its solubility groups, fully maintaining the device efficiency but becoming insoluble. This feature allows to enhance the OLED performance by applying an additional bathophenanthroline hole blocking layer from solution or by incorporating a low-molecular weight electron transport moiety into the affixing polymer matrix.     

Unmodified small-molecule organic light-emitting diodes by blade coating

Blade coating with substrate heating and hot wind is demonstrated to be a general platform for multi-layer deposition of unmodified small-molecule organic semiconductors. Most unmodified small molecules, originally designed for vacuum evaporation, can be blade coated while the solubility is above 0.5 wt.%. High uniformity is achieved for scale over 5 cm. Orange devices by evaporation and blade coating are compared with 4,4′-bis(carbazol-9-yl)biphenyl (CBP) as the host, iridium(III) bis(4-(4-t-butylphenyl)thieno[3,2-c]pyridinato-N,C²′)acetylacetonate (PO-01-TB) as the emitter. The efficiency difference is within 10%. When 2,6-bis(3-(9H-carbazol-9-yl)phenyl)pyridine (26DCzPPy) is used as the host, the current efficiencies are 40 cd/A for orange, 32 cd/A for green, and 20 cd/A for blue. The optimized organic light-emitting diodes (OLED) structure developed for vacuum deposition can therefore be exactly copied by the low cost blade coating method in solution.     

Highly Efficient Indoor Organic Photovoltaics with Spectrally Matched Fluorinated Phenylene‐Alkoxybenzothiadiazole‐Based Wide Bandgap Polymers

The unique electro‐optical features of organic photovoltaics (OPVs) have led to their use in applications that focus on indoor energy harvesters. Various adoptable photoactive materials with distinct spectral absorption windows offer enormous potential for their use under various indoor light sources. An in‐depth study on the performance optimization of indoor OPVs is conducted using various photoactive materials with different spectral absorption ranges. Among the materials, the fluorinated phenylene‐alkoxybenzothiadiazole‐based wide bandgap polymer—poly[(5,6‐bis(2‐hexyldecyloxy)benzo[c][1,2,5]thiadiazole‐4,7‐diyl)‐alt‐(5,50‐(2,5‐difluoro‐1,4‐phenylene)bis(thiophen‐2‐yl))] (PDTBTBz‐2F_anti)‐contained photoactive layer—exhibits a superior spectrum matching with indoor lights, particularly a light‐emitting diode (LED), which results in an excellent power absorption ratio. These optical properties contribute to the state‐of‐the‐art performance of the PDTBTBz‐2F_anti:[6,6]‐phenyl‐C₇₁ butyric acid methyl ester (PC₇₁BM)‐based OPV with an unprecedented high power‐conversion efficiency (PCE) of 23.1% under a 1000 lx LED. Finally, its indoor photovoltaic performance is observed to be better than that of an interdigitated‐back‐contact‐based silicon photovoltaic (PCE of 16.3%).     

Acid-functionalized fullerenes used as interfacial layer materials in inverted polymer solar cells

Two types of carboxylic acid functionalized fullerence derivatives, 4-(2-ethylhexyloxy)-[6,6]-phenyl C₆₁-butyric acid (p-EHO-PCBA) and bis-4-(2-ethylhexyloxy)-[6,6]-phenyl C₆₁-butyric acid (bis-p-EHO-PCBA), were synthesized and investigated as an interfacial layer for inverted polymer solar cells (iPSCs). The –COOH groups on the PCBAs chemisorb to inorganic metal oxide (TiO_X), generating fullerene-based self-assembled monolayers (FSAMs). The devices with the mono- and bis-FSAMs exhibited substantially lower series resistance (R_S) values of 2.10 Ω cm² and 1.46 Ω cm², compared to that (4.15 Ω cm²) of the unmodified device. The TiO_X films modified with mono- and bis-FSAMs showed higher contact angles of 50° and 91°, respectively, than that of the pristine TiO_X film (33°). The increased contact angles were attributed to the enhanced hydrophobicity, improving the wetting properties with the organic photoactive layer. In addition, a comparison of device characteristics with electroactive FSAMs and non-electroactive benzoic acid SAMs clearly indicates that the FSAMs may suggest an additional pathway for photo-induced charge transfer and charge collection to ITO. After surface modification with FSAMs, the short-circuit current density (J_SC) and fill factor (FF) values increased substantially. The iPSCs based on poly(5,6-bis(octyloxy)-4-(thiophen-2-l)benzo[c][1,2,5]thiadiazole) (PTBT) and [6,6]phenyl-C₆₁-butyric acid methyl ester (PCBM) as an active layer showed remarkably improved power conversion efficiency up to 5.13% through incorporation of the FSAMs-based interfacial layer.