Positional Effects of Fluorination in Conjugated Side Chains on Photovoltaic Properties of Donor-Acceptor Copolymers

The position at which conjugated side chains were fluorinated, the meta- or ortho-position in phenyl side chains, was varied to investigate the positional effects of fluorination on the energy levels, crystalline ordering, and photovoltaic properties of the polymers. The fluorine in the ortho-position achieved a lower HOMO energy level than that in the meta-position, but reduced the chain rigidity.1116Ysciescopu

Kalman-Filter-Based Tension Control Design for Industrial Roll-to-Roll System

This paper presents a robust and precise tension control method for a roll-to-roll (R2R) system. In R2R processing, robust and precise tension control is very important because improper web tension control leads to deterioration in the quality of web material. However, tension control is not easy because the R2R system has a model variation in which the inertia of the web in roll form is changed and external disturbances caused by web slip and crumpled web. Therefore, a disturbance observer (DOB) was proposed to achieve robustness against model variations and external disturbances. DOB is a robust control method widely used in various fields because of its simple structure and excellent performance. Moreover, the web passes through various process steps to achieve the finished product in the R2R process. Particularly, it is important to track the tension when magnitude of the tension varies during process. Feedforward (FF) controller was applied to minimize the tracking error in the transient section where tension changes. Moreover, the signal processing of a sensor using the Kalman filter (KF) in the R2R system greatly improved control performance. Finally, the effectiveness of the proposed control scheme is discussed using experimental results

High absorption coefficient ?-conjugation-extended donor -acceptor copolymers for ternary -blend solar cells

11Nsciescopu

Medium-Bandgap Conjugated Polymers Containing Fused Dithienobenzochalcogenadiazoles : Chalcogen Atom Effects on Organic Photovoltaics

We designed, synthesized, and characterized a series of three medium-bandgap conjugated polymers (PBDTfDTBO, PBDTfDTBT, and PBDTfDTBS) consisting of fused dithienobenzochalcogenadiazole (fDTBX)-based weak electron-deficient and planar building blocks, which possess bandgaps of ∼2.01 eV. The fDTBX-based medium-bandgap polymers exhibit deep-lying HOMO levels (∼5.51 eV), which is beneficial for use in multijunction polymer solar cell applications. The resulting polymers with chalcogen atomic substitutions revealed that the difference in the electron negativity and atomic size of heavy atoms highly affects an intrinsic property, morphological feature, and photovoltaic property in polymer solar cells. The polymer solar cells based on sulfur-substituted medium-bandgap polymer showed power conversion efficiencies above 6% when blended with [6,6]-phenyl-C71-butyric acid methyl ester in a typical bulk-heterojunction single cell. These results suggest that the fDTBX-based medium-bandgap polymer is a promising alternative material for P3HT in tandem polymer solar cells for achieving high efficiency.117sciescopu

pi-Extended donor-acceptor conjugated copolymers for use as hole transporting materials in perovskite solar cells

We introduced 3-octylthiophene (OT) or 3-octylthieno [3,2-b]thiophene (OTT) as pi-bridges into PBT (poly(1-(4,8-bis(5- (2-ethylhexyl)selenophen-2-yl)benzo[1,2-b:4,5-b']dithiophen-2-yl)-5-(2-butyloctyl)-4H-thieno[3,4-c] pyrrole-4,6(5H)-dione), which is based on benzodithiophene and thienopyrmlodione units, in order to prepare thiophene-based pi-bridging donor-acceptor conjugated copolymers for use as hole-transport layers in pemvskite solar cells (PeSCs). The resulting polymers exhibit strengthened intermolecular pi-pi stacking and increased crystallinity (dominant face-on orientation), which facilitates vertical charge transport and hole mobility. Moreover, the highest occupied molecular orbital level of PBT-OTT is similar to the valence band of the perovskite material. As a result, efficient hole extraction occurs with reduced charge carrier recombination in PBT-OTT-based PeSCs. Therefore, the introduction of pi-bridges to extend the pi-conjugation length of conjugated polymers is a promising strategy for the development of efficient hole-transporting materials for use in PeSCs.11Nsciescopu

Synergistic effects of an alkylthieno 3,2-b thiophene pi-bridging backbone extension on the photovoltaic performances of donor-acceptor copolymers

The synergistic effects of a thiophene-based pi-bridging backbone extension on the intrinsic and photovoltaic properties of electron donor-acceptor (D-A) copolymers were systematically investigated. A series of alternating D-A copolymers (PBTs) based on 4,8-bis(5-ethylhexylselenophen-2-yl)benzo[1,2-b:4,5-b']dithiophene (EHSeBDT) and 5-(2-butyloctyl)-4H-thieno[3,4-c]pyrrole-4,6(5H)-dione (BOTPD), which featured thiophene-based pi-bridges, were synthesized: PBT without a pi-bridge, PBT with a 3-octylthiophene (OT) pi-bridge (PBT-OT), and PBT with a 3-octylthieno[3,2-b]thiophene (OTT) pi-bridge (PBT-OTT). The light absorption and charge transport properties were significantly enhanced upon incorporation of the OTT pi-bridge. The enhancements resulted from the strong pi-pi intermolecular interactions using the OTT pi-bridging backbone extension between neighboring polymer chains. PBT-OTT was most miscible in PC71BM. As a result, the photoactive layers prepared using PBT-OTT and PC71BM formed a well-mixed bulk-heterojunction morphology and yielded organic solar cells (OSCs) with a high power conversion efficiency of 7.21%. Transient absorption analysis suggested that the mu-electrons were further delocalized along the copolymer after incorporation of the OTT pi-bridge, and the charge separation efficiency increased. These results suggested that incorporating OTT pi-bridges into D-A copolymers provides a useful strategy for developing highly efficient OSCs.118Nsciescopu

Broadband Virtual-Stub Doherty Power Amplifier Using Asymmetric Structure

The load networks of advanced Doherty power amplifiers (DPAs) have traditionally been designed according to the ABCD parameters. In this paper, design conditions as an impedance transformation condition and an effective electrical length were used to design the output matching networks (OMNs) for the carrier and peaking amplifiers of the virtual-stub DPAs (VS-DPAs). An optimization method for the effective electrical length was proposed that was specifically constructed for the load impedances of the carrier amplifier at the low power level to have broadband characteristics through the load-pull simulation. Using the optimized design conditions for broadband design, compact OMNs for the carrier and peaking amplifiers were designed using quasi-lumped components. Moreover, an asymmetric structure with an increased power capacity of the peaking amplifier for the VS-DPA was proposed to compensate for a relatively low peak fundamental current of the peaking amplifier due to its deep class-C operation as well as the extended output back-off (OBO) range of the VS-DPA. To verify the proposed load network, a broadband asymmetric VS-DPA for the 3.3 - 4.2 GHz band was designed and implemented using GaN HEMTs with power capacities of 6 and 10 W. Using a 5G new radio (5G NR) signal with a signal bandwidth of 100 MHz and a peak-to-average power ratio (PAPR) of 7.8 dB, power gain of 8.2 - 9.1 dB, DE of 46.0 - 57.0%, ACLR of better than −45 dBc after DPD linearization at an average power of 35.0 dBm were achieved at the broad frequency range of 3.3 - 4.2 GHz

Two-Dimensionally Extended π‑Conjugation of Donor–Acceptor Copolymers via Oligothienyl Side Chains for Efficient Polymer Solar Cells

A series of two-dimensional conjugated polymers containing π-conjugated oligothienyl side chains, namely PBDT2FBT-T1, PBDT2FBT-T2, PBDT2FBT-T3, and PBDT2FBT-T4, was designed and synthesized to investigate the effect of two-dimensionally extended π-conjugation on the polymer solar cell (PSC) performance. The oligothienyl units introduced into the side chains significantly affect the optoelectronic properties of the parent polymers as well as the performances of the resulting solar cell devices by altering the molecular arrangement and packing, crystalline behavior, and microstructure of the polymer:PC₇₁BM blend films. The crystallinity and blend morphology of the polymers can be systematically controlled by tuning the π-conjugation length of side chains; PBDT2FBT-T3 exhibited the most extended UV/vis light absorption band and the highest charge mobility, leading to a high short-circuit current density up to 12.5 mA cm^–2 in the relevant PSCs. The PBDT2FBT-T3:PC₇₁BM-based PSC exhibited the best power conversion efficiency of 6.48% among this series of polymers prepared without the use of processing additives or post-treatments. These results provide a new possibility and valuable insight into the development of efficient medium-bandgap polymers for use in organic solar cells