High-Performance Ambient-Condition-Processed Polymer Solar Cells and Organic Thin-Film Transistors.

Large-scale commercial synthesis of bulk-heterojunction (BHJ) solar cell materials is very challenging and both time and energy consuming. Synthesis of π-conjugated polymers (CPs) with uniform batch-to-batch molecular weight and low dispersity is a key requirement for better reproducibility of high-efficiency polymer solar cells. Herein, a conjugated polymer (CP) PTB7-Th, well known for its high performance, has been synthesized with high molecular weight and low dispersity in a closed microwave reactor. The microwave reaction procedure is known to be more controlled and consumes less energy. The precursors were strategically reacted for different reaction time durations to obtain the optimum molecular weight. All different CPs were well characterized using 1H NMR, gel permeation chromatography (GPC), UV-vis, photoluminescence (PL), electron spin resonance (ESR), and Raman spectroscopy, whereas the film morphology was extensively studied via atomic force microscopy (AFM) and grazing incidence X-ray diffraction (GIXRD) techniques. The effect of molecular weight on a conventional BHJ solar cell with PC71BM acceptor was investigated to derive systematic structure-property relationships. The CP obtained after 35 min of reaction time and integrated into BHJ devices under ambient conditions provided the best performance with a power conversion efficiency (PCE) of 8.09%, which was quite similar to the results of CPs synthesized via a thermal route. An enhanced PCE of 8.47% was obtained for the optimized polymer (35 min microwave reaction product) when device fabrication was carried out inside a glovebox. The organic thin-film transistor (OTFT) device with the microwave-synthesized CP displayed better hole mobility (0.137 cm2 V-1 s-1) as compared to that with the thermally synthesized CP. This study also proved that the device stability and reproducibility of the microwave-synthesized CP were much better and more consistent than those of the thermally developed CP.

Conjugated Polymer-Based Electrical Sensor for Ultratrace Vapor-Phase Detection of Nerve Agent Mimics.

Considering the vital need to strengthen the national security emanating from chemical threats, a low-cost, portable ultrasensitive electrical sensor for real-time monitoring of diethylchlorophosphate (DCP) (nerve gas mimic) has been developed. The device consists of a "simple to be fabricated" two-terminal resistor and an electronic combinational circuit for rapid onsite detection of lethal nerve gas vapors with high degree of accuracy in milliseconds. This device is a smart readout electronic model that detects ultratrace DCP vapors by bright visual alerts from light-emitting diode (LED) and loud alarm signal without the need for employing a sophisticated instrument. To obtain high sensitivity and discriminating response, a novel amine-functionalized conjugated polymer (CP) is designed as a sensory channel material for two-terminal sensor. The low-powered poly(3-(9,9-dioctyl-9H-fluoren-2-yl)benzene-1,2-diamine) (PFPDA) fabricated two-terminal electrical sensor is tested at ambient conditions, which shows excellent sensitivity toward nerve gas mimic DCP, with a rapid response in 3 s and a very low limit of detection (LOD) of 5.88 ppb. The amine moiety of PFPDA CP plays a vital role in redox interaction between the semiconductor CP and organophosphates, which ultimately leads to the amplified current signal. The redox interactions occurring among the organophosphate analytes and the amine functional group on the PFPDA backbone provided insights into the mechanism of sensing, which formed the basis of the excellent sensitivity and discriminating ability of this sensor device. The newly designed PFPDA CP-based portable electrical sensor device demonstrates a key contribution in the field of portable electronics for defense safety and environmental monitoring applications.

Effect of fluorine substitution and position on phenylene spacer in carbazole based organic sensitizers for dye sensitized solar cells.

The preparation of a series of organic dyes having a carbazole donor, cyanoacrylic acid as an acceptor, and phenylene ring as a spacer with the difference in the positions of fluorine substitution is reported. Due to its unique properties of small size and high electronegativity, fluorine is now being extensively used to control the optoelectronic properties of organic conjugated materials. In this study, the results revealed that the specific position and number of fluorine substitution were very crucial to control the optical as well as the electrochemical properties of organic dyes. It was found that fluorine substitution led to a redshift in the absorption spectra of the dyes and reduced the band gap. The injection rate of photoexcited electrons was measured using time-resolved photoluminescence and the o-fluoro substituted dye MA1F-o showed the best electron injection dynamics. As a result of broad absorption and high electron injection rate, the dye MA1F-o outperformed other dyes with a power conversion efficiency of 4.02% (Jsc = 8.3 mA cm-2, Voc = 0.75 V and FF = 0.64). The non-fluorinated dye MA0F exhibited a power conversion efficiency of 3.23% (Jsc = 6.8, Voc = 0.72 and FF = 0.67). The dye MA1F-m exhibited the least molar absorption coefficient and a lower power conversion efficiency because of the meta inductive effect.