Jiake Wu

Solution-grown organic single-crystalline p-n junctions with ambipolar charge transport.

Organic single-crystalline p-n junctions are grown from mixed solutions. First, C60 crystals (n-type) form and, subsequently, C8-BTBT crystals (p-type) nucleate heterogeneously on the C60 crystals. Both crystals continue to grow simultaneously into single-crystalline p-n junctions that exhibit ambipolar charge transport characteristics. This work provides a platform to study organic single-crystalline p-n junctions.

Boosting the electron mobility of solution-grown organic single crystals via reducing the amount of polar solvent residues

Enhancing electron transport to match with the development in hole transport is critical for organic electronics in the future. As electron motion is susceptible to extrinsic factors, seeking these factors and avoiding their negative effects have become the central challenge. Here, the existence of polar solvent residues in solution-grown single-crystals of 6,13-bis(triisopropylsilylethynyl)-5,7,12,14-tetraazapentacene is identified as a factor detrimental to electron motion. Field-effect transistors of the crystals exhibit electron mobility boosted by about 60% after the residues are removed. The average electron mobility reaches up to 8.0 ± 2.2 cm2 V−1 s−1 with a highest value of 13.3 cm2 V−1 s−1; these results are significantly higher than those obtained previously for the same molecule (1.0–5.0 cm2 V−1 s−1). Furthermore, the achieved mobility is also higher than the maximum reported electron mobility for organic materials (11 cm2 V−1 s−1). This work should greatly accelerate the advancement of organic electron-transporting materials.

Ambipolar charge transport of TIPS-pentacene single-crystals grown from non-polar solvents

Charge transport of solution-grown TIPS-pentacene single-crystals depends on the polarity of the used solvents. Crystals grown from non-polar solvents exhibit ambipolar transport (μe 0.020 cm2 V−1 s−1; μh 5.0 cm2 V−1 s−1), while polar solvents suppress electron transport. This work indicates that appropriate selection of solvents should further harvest the n-type behaviors of organic semiconductors.

Interfacing Solution-Grown C60 and (3-Pyrrolinium)(CdCl3 ) Single Crystals for High-Mobility Transistor-Based Memory Devices.

Aligned ferroelectric single crystals of (3-pyrrolinium)(CdCl3 ) can be prepared from solution on top of aligned semiconducting C60 single crystals using an orthogonal solvent. Memory devices based on these ferroelectric/semiconductor bilayered heterojunctions exhibit much larger hysteresis compared with that of only C60 single crystals. More importantly, the introduction of the ferroelectric layer induces the memory window without dramatically reducing the charge mobility.

Preparation of Single-Crystalline Heterojunctions for Organic Electronics

Organic single-crystalline heterojunctions are composed of different single crystals interfaced together. The intrinsic highly ordered heterostructure in these multicomponent solids holds the capacity for multifunctions, as well as superior charge-transporting properties, promising high-performance electronic applications such as ambipolar transistors and solar cells. However, this kind of heterojunction is not easily available and the preparation methods need to be developed. Recent advances in the efficient strategies that have emerged in yielding high-quality single-crystalline heterojunctions are highlighted here. The advantages and limitations of each strategy are also discussed. The obtained single-crystalline heterojunctions have started to exhibit rich physical properties, including metallic conduction, photovoltaic effects, and so on. Further structural optimization of the heterojunctions to accommodate the electronic device configuration is necessary to significantly advance this research direction.

Single-crystalline lead halide perovskite arrays for solar cells

We have successfully grown single-crystalline lead halide perovskite arrays on a poly(3,4-ethylene dioxythiophene):polystyrenesulfonic acid (PEDOT:PSS) coated ITO substrate by the droplet-pinned crystallization (DPC) method and, for the first time, single-crystalline perovskite solar cells have been fabricated with a power conversion efficiency of 1.73%.

A matrix-based Bayesian approach for manufacturing resource allocation planning in supply chain management

Nowadays, the supply chain of manufacturing resources is typically a large complex network, whose management requires network-based resource allocation planning. This paper presents a novel matrix-based Bayesian approach for recommending the optimal resource allocation plan that has the largest probability as the optimal selection within the context specified by the user. A proposed matrix-based representation of the resource allocation plan provides supply chain modelling with a good basis to understand problem complexity, support computer reasoning, facilitate resource re-allocation, and add quantitative information. The proposed Bayesian approach produces the optimal, robust manufacturing resource allocation plan by solving a multi-criteria decision-making problem that addresses not only the ontology-based static manufacturing resource capabilities, but also the statistical nature of the manufacturing supply chain, i.e. probabilities of resource execution and resource interaction execution. A genetic algorithm is employed to solve the multi-criteria decision-making problem efficiently. We use a case study from manufacturing domain to demonstrate the applicability of the proposed approach to optimal manufacturing resource allocation planning.

Low temperature processed ITO-free perovskite solar cells without a hole transport layer

Perovskite solar cells (PSCs) have been considered as a promising photovoltaic technology due to their attractive power conversion efficiency (PCE) exceeding 20% and ease of processability at low temperature. However, there have been a few reports on low temperature processed ITO-free PSCs. In this work, highly transparent and conductive poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (HC-PEDOT:PSS, PH1000) was employed as electrode as an alternative material to ITO. PSCs built on three different electrodes (PH1000-5%, PH1000-10% and PH1000-H) with or without a hole transport layer (HTL) were fabricated. The factors that influence the performance of PSCs such as conductivity, morphology, work function and wettability of the electrode, morphology of perovskite films and different electrode treatments were investigated. A comparison of different electrodes as well as their corresponding impact on the device performance were also presented. The optimized average PCE of 7.95% with the highest PCE up to 9.65% for PSCs built on the PH1000-10% electrode without HTL were achieved. When a layer of PEDOT:PSS was spin coated on PH1000-H to prevent perovskite from decomposing, the optimized PCE of 6.98% with the highest up to 9.31% was achieved. Our results indicate that PH-1000 is a promising material to replace both ITO electrode and HTL, providing a much simpler architecture for flexible PSC applications.

Enhanced performance of field-effect transistors based on C 60 single crystals with conjugated polyelectrolyte

Contact resistance at the interface between metal electrodes and semiconductors can significantly limit the performance of organic field-effect transistors, leading to a distinct voltage drop at the interface. Here, we demonstrate enhanced performance of n-channel field-effect transistors based on solution-grown C60 single-crystalline ribbons by introducing an interlayer of a conjugated polyelectrolyte (CPE) composed of poly[(9,9-bis(3′-((N,N-dimethyl)-N-ethylammonium)-propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)] dibromide (PFN+Br−). The PFN+Br− interlayer greatly improves the charge injection. Consequently, the electron mobility is promoted up to 5.60 cm2 V−1 s−1 and the threshold voltage decreased dramatically with the minimum of 4.90 V.