Feng Ge

Organic Field-Effect Transistors with Macroporous Semiconductor Films as High-Performance Humidity Sensors

In this study, we designed and fabricated a high-performance humidity sensor based on a donor-acceptor polymer transistor. To improve its sensing performance, a polymeric semiconductor film with macroporous structure was prepared using a facilitated phase-separation method. The relationship between the sensing performance and the pore size was systematically investigated by testing the humidity-sensing performance. The results suggested that the sensitivity of the sensor was improved with increasing pore size within a certain range. The sensor based on the macroporous film with an average pore size of 154 nm exhibited a sensitivity of 415 and a response time of 0.68 s, as the low relative humidity (RH) changed from 32% RH (9146 ppm) to 69% RH (20 036 ppm). These sensitivity values are better than those obtained by other reported humidity sensors based on organic field-effect transistors.

Bis(2-oxo-7-azaindolin-3-ylidene)benzodifuran-dione-based donor–acceptor polymers for high-performance n-type field-effect transistors

Two donor–acceptor (D–A) conjugated polymers, PBABDF-DT and PBABDF-TVT, were synthesized using a strongly electron-deficient unit, (3E,7E)-3,7-bis(6-bromo-1-(4-decyltetradecyl)-2-oxo-7-azaindolin-3-ylidene)benzo[1,2-b:4,5-b′]difuran-2,6(3H,7H)-dione (BABDF) as the acceptor, and dithiophene and (E)-2-(2-(thiophen-2-yl)vinyl)thiophene as the donor units. Both polymers exhibited low LUMO energy levels (∼−4.0 eV) for marching with electron transport and displayed excellent n-type charge transport characteristics. The organic field-effect transistors exhibited the highest electron mobilities of 1.86 cm2 V−1 s−1 and 1.56 cm2 V−1 s−1 with high Ion/Ioff ratios of 1.6 × 106 and 1.0 × 106 for PBABDF-DT and PBABDF-TVT, respectively. Both polymers had highly uniform polymer nanofibers, orderly lamellar crystalline structures, and close π–π stacking distances which all contributed to the high charge carrier mobility.

Tailoring Structure and Field-Effect Characteristics of Ultrathin Conjugated Polymer Films via Phase Separation

A phase-separation method has been developed to control the semiconductor thickness and molecular arrangement via the semiconducting/insulating polymer blend system. The thickness of the poly(3-hexylthiophene) film has been regulated from 10.5 ± 1.4 nm down to 1.9 ± 0.8 nm with a favorable self-assembly degree and the mobility ranging from 0.21 to 0.03 cm2 V-1 s-1. The ultrathin films show high bias stability and weak decay after 24 days with a bottom-gate configuration. Benefited from a good molecular order, the films have low activation energy and a 2D charge transport profile in semiconductor layers. Moreover, this blending process can be used as a general strategy of thickness control in flexible low-voltage devices and donor-acceptor-conjugated polymers.

One-pot synthesized ABA tri-block copolymers for high-performance organic field-effect transistors

A series of P3HT-b-PHA-b-P3HT tri-block and P3HT-b-PHA di-block copolymers were facilely synthesized in one pot. The influence of the block ratio on the optical, microstructural and electrical properties has been investigated. OFETs based on these block copolymers have been fabricated with an improved mobility of 0.052 cm2 V−1 s−1via a blending method.

FePc induced highly oriented PIID-BT conjugated polymer semiconductor with high bias-stress stability

Polymer semiconductors with high crystallinity and high molecular orientation have been demonstrated to be in favor of improving the bias-stress stability of organic field-effect transistors (OFETs). The isoindigo (IID)-bithiophene (BT) based conjugated polymer (PIID-BT) is a typical donor–acceptor polymer with higher hole mobility and can be used for the bias-stress stability study. In this work, we use a small organic molecule of FePc to optimize the morphology and structure of the PIID-BT semiconductor to improve the bias-stress stability of OFET devices. The high crystallinity and ordered morphology of the FePc-doped PIID-BT film are realized, and this as-obtained FePc-doped PIID-BT OFET shows more outstanding bias-stress stability, with a lower drain current decay of only 12% over a stressing time of 1000 s than that of ca. 50% for the pristine PIID-BT devices. The electronic structure features reveal the bind between FePc and PIID-BT molecules via the Fe-O coordination interaction, which would be responsible for the efficiently oriented growth of the PIID-BT polymer and eventually promote the bias-stress stability of PIID-BT based OFET devices.Polymer semiconductors with high crystallinity and high molecular orientation have been demonstrated to be in favor of improving the bias-stress stability of organic field-effect transistors (OFETs). The isoindigo (IID)-bithiophene (BT) based conjugated polymer (PIID-BT) is a typical donor–acceptor polymer with higher hole mobility and can be used for the bias-stress stability study. In this work, we use a small organic molecule of FePc to optimize the morphology and structure of the PIID-BT semiconductor to improve the bias-stress stability of OFET devices. The high crystallinity and ordered morphology of the FePc-doped PIID-BT film are realized, and this as-obtained FePc-doped PIID-BT OFET shows more outstanding bias-stress stability, with a lower drain current decay of only 12% over a stressing time of 1000 s than that of ca. 50% for the pristine PIID-BT devices. The electronic structure features reveal the bind between FePc and PIID-BT molecules via the Fe-O coordination interaction, which would be re...

Bar-Coated Ultrathin Semiconductors from Polymer Blend for One-Step Organic Field-Effect Transistors

One-step deposition of bi-functional semiconductor-dielectric layers for organic field-effect transistors (OFETs) is an effective way to simplify the device fabrication. However, the proposed method has rarely been reported in large-area flexible organic electronics. Herein, we demonstrate wafer-scale OFETs by bar coating the semiconducting and insulating polymer blend solution in one-step. The semiconducting polymer poly(3-hexylthiophene) (P3HT) segregates on top of the blend film, whereas dielectric polymethyl methacrylate (PMMA) acts as the bottom layer, which is achieved by a vertical phase separation structure. The morphology of blend film can be controlled by varying the concentration of P3HT and PMMA solutions. The wafer-scale one-step OFETs, with a continuous ultrathin P3HT film of 2.7 nm, exhibit high electrical reproducibility and uniformity. The one-step OFETs extend to substrate-free arrays that can be attached everywhere on varying substrates. In addition, because of the well-ordered molecular arrangement, the moderate charge transport pathway is formed, which resulted in stable OFETs under various organic solvent vapors and lights of different wavelengths. The results demonstrate that the one-step OFETs have promising potential in the field of large-area organic wearable electronics.

Helical Nanofibrils of Block Copolymer for High-Performance Ammonia Sensors

Conjugated polymers with a helical structure have been in rapid development in recent years because of their potential applications in chemical and biological sensors. We demonstrate the fabrication and characterization of helical nanofibrils of block copolymer poly(4-iso-cyano-benzoic acid 5-(2-dimethylamino-ethoxy)-2-nitro-benzylester)- b-poly(3-hexylthiophene) (PPI(-DMAENBA)- b-P3HT) via a transfer-etching method. The density and lateral length of nanofibrils can be facilely controlled by regulating the process conditions, which, in turn, directly determine the electronic property. Organic field effect transistors based on helical nanofibrils were successfully fabricated with the highest mobility of 9.1 × 10-3 cm2/(V s)-1, an on/off ratio of 3.4 × 105, and high bias stability. The helical nanofibrils were proved to be beneficial for obtaining a highly sensitive and selective chemical sensor. And, the transistor based on helical nanofibrils exhibits a relative response of 28.6% to 100 ppb ammonia, which is even much higher than the responses to 1 ppm ammonia for homo poly(3-hexylthiophene) nanofibrils (7%) and block copolymer nanofibrils without helical structure (0.9%). The combination of helical structure with nanofibrils may provide a new strategy to fabricate high-performance chemical sensors suitable for use in environmental monitoring, industrial and agricultural production, health care, and foodsafety.

Correction to “Organic Field-Effect Transistors with Macroporous Semiconductor Films as High-Performance Humidity Sensors”

Semiconductor Films as High-Performance Humidity Sensors” Shaohua Wu, Guiheng Wang, Zhan Xue, Feng Ge, Guobing Zhang, Hongbo Lu, and Longzhen Qiu* ACS Appl. Mater. Interfaces 2017, 9 (17), 14974−14982. DOI: 10.1021/acsami.7b01865 D to a production error, Figure 7 is the wrong picture at page 14980. The correct Figure 7 is as follows. The change does not effect the scientific conclusions of the paper.