Dithieno[2,3-d;2 ',3 '-d ']benzo[1,2-b;4,5-b ']-dithiophene based organic sensitizers for dye-sensitized solar cells

We report two novel D-pi-A type organic dyes with a coplanar dithieno[2,3-d; 2',3'-d']benzo[1,2 b;4,5-b']dithiophene (DTBDT) as pi-spacer for dye-sensitized solar cells. A best device performance with a power conversion efficiency of 6.32% is achieved, making DTBDT unit a promising building block for design of organic sensitizers

der Johannes Gutenberg Universität

vorgelegt vo

Optoelectronic and/or electrochemical learning device

The present invention concerns photoelectronic and/or optoelectronic learning device and/or memory device. In an embodiment, the device is a dye- sensitized solar cell. The short circuit photocurrent density (Jsc) of the device, and wherein a degree of a Jsc drop, depends on how long the device is being illuminated. During a subsequent absence of illumination, Jsc of the device increases in a time dependent manner. Furthermore, said degree of Jsc drop depends on the number of cycles of successive illumination and absence of illumination. The device of the invention may be considered as a self-evolving hardware that translates learning into long lasting changes in electronic parameters, akin to the neuronal network in the human brain. The device of the invention mimics traits of intelligent learning through optical stimulus. Particularly, the device exhibits and memorizes variations in its electronic properties differently, depending on the duration and the repetition rate of previous light exposure

Illumination Time Dependent Learning in Dye Sensitized Solar Cells

Learning through vision is an essential skill for intelligent machines. In an attempt to implement this highly complex feature at low energy cost, a dye-sensitized solar cell is proposed that learns using illumination time as a cue. Particularly, the device alters its photocurrent and memorizes this change in dependence of light exposure duration. This behavior parallels synaptic learning that also requires continuous or repeated electrical stimuli as triggers. Therefore, such optically learning solar cells may serve as promising building blocks in optoelectronic neural networks, potentially enabling visually learning electronics operating at negligible energy consumption and minimal hardware complexity

Avoiding Diffusion Limitations in Cobalt(III/II)-Tris(2,2'-Bipyridine)-Based Dye-Sensitized Solar Cells by Tuning the Mesoporous TiO2 Film Properties

Dye-sensitized solar cells based on electrolytes containing cobalt complexes as redox shuttles typically suffer a major limitation in terms of slow diffusion of those couples through the mesoporous TiO2 film. This results in a drop of the photocurrent density, particularly at high incident light intensities, reducing the overall cell performance. This work illustrates how tuning the four characteristic parameters of the mesoporous TiO2 layer, namely film thickness, particle size, pore size and porosity, by simply optimizing the TiCl4 post-treatment, completely eliminates diffusion problems of cobalt(III/II) tris(2,2'-bipyridine) and at the same time maximizes the short-circuit photocurrent density. As a result, a power conversion efficiency of 10.0?% at AM 1.5 G 100 mW?cm-2 was reached in conjunction with an organic sensitizer

A Computer Vision Sensor for Efficient Object Detection Under Varying Lighting Conditions

Convolutional neural networks (CNNs) have attracted much attention in recent years due to their outstanding performance in image classification. However, changes in lighting conditions can corrupt image segmentation conducted by CNN, leading to false object detection. Even though this problem can be mitigated using a more extensive CNN training set, the immense computational and energy resources required to continuously run CNNs during always‐on applications, such as surveillance or self‐navigation, pose a serious challenge for battery‐reliant mobile systems. To tackle this longstanding problem, a vision sensor capable of autonomously correcting for sudden variations in light exposure, without invoking any complex object detection software, is proposed. Such video preprocessing is efficiently achieved using photovoltaic pixels tailored to be insensitive to specific ranges of light intensity alterations. In this way, the pixels behave similarly to neurons, wherein the execution of object detection software is only triggered when light intensities shift above a certain threshold value. This proof‐of‐concept device allows for efficient fault‐tolerant object detection to be implemented with reduced training data as well as minimal energy and computational costs and demonstrates how hardware engineering can complement software algorithms to improve the overall energy efficiency of computer vision

Fine-tuning the Electronic Structure of Organic Dyes for Dye-Sensitized Solar Cells

A series of metal-free organic dyes exploiting different combinations of (hetero)cyclic linkers (benzene, thiophene, and thiazole) and bridges (4H-cyclopenta[2,1-b:3,4-b']dithiophene (CPDT) and benzodithiophene (BDT)) as the central pi-spacers were synthesized and characterized. Among them, the sensitizer containing the thiophene and CPDT showed the most broad incident photon-to-current conversion efficiency spectra, resulting in a solar energy conversion efficiency (eta) of 6.6%

Extended pi-Bridge in Organic Dye-Sensitized Solar Cells: the Longer, the Better?

The elongation of pi-conjugated bridges between the donor (D) and the acceptor (A) represents a feasible strategy towards enhancement of light-harvesting in both breadth and depth of organic D-pi-A dyes suitable for nanocrystalline TiO2-based dye-sensitized solar cells (DSSCs). Here, a series of organic dyes with elongating conjugated bridges is synthesized and characterized. DSSC devices employing a cobalt (II/III) redox electrolyte are fabricated using these dyes as light-harvesting sensitizers. Compared to a dye with the 3,4-ethylenedioxythiophene (EDOT) linker (G188), the three counter-parts with further extended pi-bridges present gradually red-shifted electronic absorption spectra and a persistent decrease in oxidation potential. The photocurrent action spectra show that the extension of pi-conjugated bridges decreases the open-circuit photovoltage. The best performance is shown in G268 with a short-circuit photocurrent density (J(sc)) of 16.27 mA cm(2), an open-circuit photovoltage (V-oc) of 0.83 V, and a fill factor (FF) of 0.67, corresponding to an overall conversion efficiency of 9.24%. Unexpectedly, G270, which has with the longest pi-bridge, showed the lowest J(sc), V-oc, and efficiency

Field-effect transistors based on a benzothiadiazole-cyclopentadithiophene copolymer

We present a solution processed organic field-effect transistor based on a benzothiadiazole (BTZ)cyclopentadithiophene (CDT) copolymer with mobilities as high as 0.17 cm(2)/Vs and an on/off ratio of 10(5). This pronounced performance together with the lack of macroscopic order in the thin film makes this conjugated copolymer an attractive candidate for low-cost organic electronics due to its facile processing.close27426

Influence of the interfacial charge-transfer resistance at the counter electrode in dye-sensitized solar cells employing cobalt redox shuttles

We highlight the effect of the interfacial charge-transfer resistance at the counter electrode in dye-sensitized solar cells based on two cobalt redox shuttles, namely cobalt(III/II) tris(2,2'-bipyridine) and cobalt(III/II) tris(1,10-phenanthroline). Highly porous counter electrodes based on poly(3,4-ethylenedioxythiophene) (PEDOT) prepared by electro-oxidative polymerization are compared to the typically employed platinized FTO glass, with the former showing much lower charge transfer resistances for both cobalt complexes, leading to improved fill factors and to linear response of the short circuit photo-current density to light intensity up to one sun. Based on these findings, an excellent power conversion efficiency of 10.3% was achieved with a recently reported organic sensitizer and PEDOT as counter electrode