Dong-Yu Kim

Precise Side-Chain Engineering of Thienylenevinylene–Benzotriazole-Based Conjugated Polymers with Coplanar Backbone for Organic Field Effect Transistors and CMOS-like Inverters

Two donor-acceptor (D-A) alternating conjugated polymers based on thienylenevinylene-benzotriazole (TV-BTz), PTV6B with a linear side chain and PTVEhB with a branched side chain, were synthesized and characterized for organic field effect transistors (OFETs) and complementary metal-oxide-semiconductor (CMOS)-like inverters. According to density functional theory (DFT), polymers based on TV-BTz exhibit a coplanar and rigid structure with no significant twists, which could cause to an increase in charge-carrier mobility in OFETs. Alternating alkyl side chains of the polymers impacted neither the band gap nor the energy level. However, it significantly affected the morphology and crystallinity when the polymer films were thermally annealed. To investigate the effect of thermal annealing on the morphology and crystallinity, we characterized the polymer films using atomic force microscopy (AFM) and 2D-grazing incidence X-ray diffraction (2D-GIWAXD). Fibrillary morphologies with larger domains and increased crystallinity were observed in the polymer films after thermal annealing. These polymers exhibited improved charge-carrier mobilities in annealed films at 200 °C and demonstrated optimal OFET device performance with p-type transport characteristics with charge-carrier mobilities of 1.51 cm2/(V s) (PTV6B) and 2.58 cm2/(V s) (PTVEhB). Furthermore, CMOS-like inorganic (ZnO)-organic (PTVEhB) hybrid bilayer inverter showed that the inverting voltage (Vinv) was positioned near the ideal switching point at half (1/2) of supplied voltage (VDD) due to fairly balanced p- and n-channels.

One-Step Printable Perovskite Films Fabricated under Ambient Conditions for Efficient and Reproducible Solar Cells

Despite the potential of roll-to-roll processing for the fabrication of perovskite films, the realization of highly efficient and reproducible perovskite solar cells (PeSCs) through continuous coating techniques and low-temperature processing is still challenging. Here, we demonstrate that efficient and reliable CH3NH3PbI3 (MAPbI3) films fabricated by a printing process can be achieved through synergetic effects of binary processing additives, N-cyclohexyl-2-pyrrolidone (CHP) and dimethyl sulfoxide (DMSO). Notably, these perovskite films are deposited from premixed perovskite solutions for facile one-step processing under a room-temperature and ambient atmosphere. The CHP molecules result in the uniform and homogeneous perovskite films even in the one-step slot-die system, which originate from the high boiling point and low vapor pressure of CHP. Meanwhile, the DMSO molecules facilitate the growth of perovskite grains by forming intermediate states with the perovskite precursor molecules. Consequently, fully printed PeSC based on the binary additive system exhibits a high PCE of 12.56% with a high reproducibility.

Ambipolar Small-Molecule:Polymer Blend Semiconductors for Solution-Processable Organic Field-Effect Transistors

We report on the fabrication of an organic thin-film semiconductor formed using a blend solution of soluble ambipolar small molecules and an insulating polymer binder that exhibits vertical phase separation and uniform film formation. The semiconductor thin films are produced in a single step from a mixture containing a small molecular semiconductor, namely, quinoidal biselenophene (QBS), and a binder polymer, namely, poly(2-vinylnaphthalene) (PVN). Organic field-effect transistors (OFETs) based on QBS/PVN blend semiconductor are then assembled using top-gate/bottom-contact device configuration, which achieve almost four times higher mobility than the neat QBS semiconductor. Depth profile via secondary ion mass spectrometry and atomic force microscopy images indicate that the QBS domains in the films made from the blend are evenly distributed with a smooth morphology at the bottom of the PVN layer. Bias stress test and variable-temperature measurements on QBS-based OFETs reveal that the QBS/PVN blend semiconductor remarkably reduces the number of trap sites at the gate dielectric/semiconductor interface and the activation energy in the transistor channel. This work provides a one-step solution processing technique, which makes use of soluble ambipolar small molecules to form a thin-film semiconductor for application in high-performance OFETs.

A conjugated polymer with high planarity and extended π-electron delocalization via a quinoid structure prepared by short synthetic steps

An attractive synthetic strategy for incorporating a quinoidal molecule into a conjugated polymer backbone with three short steps is reported here. The quinoidal polymer, PQuBTV, exhibited high planarity and extended conjugation. As a result, ambipolar charge carrier mobilities of 0.52 cm2 V−1 s−1 for holes and 0.53 cm2 V−1 s−1 for electrons were observed in field-effect transistor devices.

Structure–property relationship of D–A type copolymers based on phenanthrene and naphthalene units for organic electronics

Four donor–acceptor (D–A) type conjugated polymers (PA1, PA2, PA3 and PA4) based on phenanthrene and naphthalene as the donating units with or without dimethoxy substitution were synthesized for organic field effect transistors (OFETs) and bulk-heterojunction organic photovoltaics (OPVs). Dimethoxy substituents have significant effects on the optical, electrochemical, charge transport and photovoltaic properties depending on the donor-polyaromatic (PA) compounds. The optical band gaps of these PA-based copolymers from the smallest to the largest are as follows: 1.52 eV (1,5-dimethoxy substituted naphthalene (PA4)), 1.59 eV (unsubstituted naphthalene (PA3)), and 1.63 eV (unsubstituted phenanthrene (PA1), and substituted 9,10-dimethoxy phenanthrene (PA2)). While the values vary depending on the compounds, both PA2 and PA4 are found to have higher highest occupied molecular orbital (HOMO) energy levels than those of PA1 and PA3 due to the electron donating nature of dimethoxy substituents. The PA based copolymers without dimethoxy substituents showed highly balanced ambipolar behavior with ∼1 cm2 V−1 s−1, whereas the electron mobility of dimethoxy modified PA (MeOPA) based copolymers was suppressed. The inverted bulk heterojunction OPVs based on PA1 and PA3 exhibited power conversion efficiency (PCE) as high as 5.3% and 5.8%, respectively. The PCEs of PA copolymer-based OPV devices were mainly affected by an increase in the open circuit voltage rather than by the photocurrent or fill factor.

Solution-processed polymer-sorted semiconducting carbon nanotube network transistors with low-k /high-k bilayer polymer dielectrics

Solution-processed semiconducting carbon nanotube transistors with a high mobility and an ON/OFF ratio are the most promising for use in flexible electronics. In this paper, we report low-k/high-k bilayer polymer dielectrics for solution-processed semiconducting single-walled carbon nanotube (s-SWNT) field-effect transistors (s-SWNT-FETs) with efficient charge transport and operation at low voltage. Thin low-k polystyrene (10u2009nm) is used for the first contact insulator with a channel in order to passivate the dipolar disorder induced by high-k insulators. The second gate insulator for low voltage operation is cyanoethyl pullulan (CEP), which is an environmentally friendly high-k insulator based on cellulose. Moreover, poly[(vinylidenefluoride-co-trifluoroethylene) is chosen as a single layer dielectric for comparison. A reasonably low operational voltage (<10u2009V) and high operational stability are achieved by the s-SWNT-FETs with polystyrene/CEP bilayer gate dielectrics. In addition, this indicates that th...

Small-Molecule Organic Photovoltaic Modules Fabricated via Halogen-Free Solvent System with Roll-to-Roll Compatible Scalable Printing Method

For the first time, the photovoltaic modules composed of small molecule were successfully fabricated by using roll-to-roll compatible printing techniques. In this study, blend films of small molecules, BTR and PC71BM were slot-die coated using a halogen-free solvent system. As a result, high efficiencies of 7.46% and 6.56% were achieved from time-consuming solvent vapor annealing (SVA) treatment and roll-to-roll compatible solvent additive approaches, respectively. After successful verification of our roll-to-roll compatible method on small-area devices, we further fabricated large-area photovoltaic modules with a total active area of 10 cm2, achieving a power conversion efficiency (PCE) of 4.83%. This demonstration of large-area photovoltaic modules through roll-to-roll compatible printing methods, even based on a halogen-free solvent, suggests the great potential for the industrial-scale production of organic solar cells (OSCs).

A systematic study on molecular planarity and D–A conformation in thiazolothiazole- and thienylenevinylene-based copolymers for organic field-effect transistors

A new donor–acceptor type conjugated polymer (P1) composed of thiazolothiazole (TzTz) and thienylenevinylene (TV) units was synthesized to confirm that structural characteristics, such as the presence of coplanar units and a D–A conformation in the polymer main chain, can have an effect on charge carrier transport in high performance organic field-effect transistors. P1 was compared with two polymers that had bithiophene (BiTh) units instead of TV units (P2) or thienothiophene (TT) units in the place of TzTz units (P3) to investigate the relationship between the molecular structure and polymer properties. P1 had a higher order of orientation than P2 due to the rigid and planar structure caused by the presence of the TV unit in P1 compared to the distorted structure of P2. The effect of the D–A type configuration in P1 was also confirmed by demonstrating its stronger intermolecular interactions and more effective hole and electron transport compared with that of the D–D type polymer P3. Thus, in contrast to P2 (with a hole mobility of 0.076 cm2 V−1 s−1 and an electron mobility of 0.0025 cm2 V−1 s−1) and P3 (with a hole mobility of 0.2 cm2 V−1 s−1 only), P1 exhibited higher ambipolar charge carrier mobilities (1.66 cm2 V−1 s−1 of holes and 0.05 cm2 V−1 s−1 of electrons).