Peng Mao

Graphdiyne:ZnO Nanocomposites for High-Performance UV Photodetectors.

Graphdiyne (GD), a novel carbon allotrope with a 2D structure comprising benzene rings and carbon-carbon triple bonds, is successfully integrated with ZnO nanoparticles by a wet chemistry method. An ultraviolet photodetector based on these graphdiyne:ZnO nanocomposites exhibits significantly enhanced performance in comparison with a conventional ZnO device. GD may have diverse applications in future optoelectronics.

Efficiency-Enhanced Planar Perovskite Solar Cells via an Isopropanol/Ethanol Mixed Solvent Process

Solution processable perovskite solar cells traditionally employed isopropanol as the solvent of CH3NH3I in a two-step method. One of the largest issues of this technique is the uncontrollable morphology of the perovskite film. In this study, a homogeneous and dense PbI2 film was prepared by introducing DMSO as an additive into DMF and then reacting the mixture with CH3NH3I dissolved in an isopropanol/ethanol solvent to fabricate high-quality perovskite films. Results revealed that ethanol played a crucial role on morphology and components of perovskite films. When the ratio of isopropanol to ethanol was optimized, a power conversion efficiency of 15.76% was achieved, which was on average ∼50% higher than that of PSCs without DMSO and ethanol processing.

Bilayer PbS Quantum Dots for High‐Performance Photodetectors

Due to their wide tunable bandgaps, high absorption coefficients, easy solution processabilities, and high stabilities in air, lead sulfide (PbS) quantum dots (QDs) are increasingly regarded as promising material candidates for next-generation light, low-cost, and flexible photodetectors. Current single-layer PbS-QD photodetectors suffer from shortcomings of large dark currents, low on-off ratios, and slow light responses. Integration with metal nanoparticles, organics, and high-conducting graphene/nanotube to form hybrid PbS-QD devices are proved capable of enhancing photoresponsivity; but these approaches always bring in other problems that can severely hamper the improvement of the overall device performance. To overcome the hurdles current single-layer and hybrid PbS-QD photodetectors face, here a bilayer QD-only device is designed, which can be integrated on flexible polyimide substrate and significantly outperforms the conventional single-layer devices in response speed, detectivity, linear dynamic range, and signal-to-noise ratio, along with comparable responsivity. The results which are obtained here should be of great values in studying and designing advanced QD-based photodetectors for applications in future flexible optoelectronics.

Temperature-dependent Schottky barrier in high-performance organic solar cells

Organic solar cells (OSCs) have attracted great attention in the past 30 years, and the power conversion efficiency (PCE) now reaches around 10%, largely owning to the rapid material developments. Meanwhile with the progress in the device performance, more and more interests are turning to understanding the fundamental physics inside the OSCs. In the conventional bulk-heterojunction architecture, only recently it is realized that the blend/cathode Schottky junction serves as the fundamental diode for the photovoltaic function. However, few researches have focused on such junctions, and their physical properties are far from being well-understood. In this paper based on PThBDTP:PC71BM blend, we fabricated OSCs with PCE exceeding 10%, and investigated temperature-dependent behaviors of the junction diodes by various characterization including current-voltage, capacitance-voltage and impedance measurements between 70 to 290 K. We found the Schottky barrier height exhibits large inhomogeneity, which can be described by two sets of Gaussian distributions.

Improving the photocurrent of a PBDTTT-CF and PCBM based organic thin film photoconductor by forming a bilayer structure

The performance of traditional organic thin film photoconductors (OTFPs) is limited by the low carrier mobility in the donor : acceptor (D : A) blend film. To overcome such a problem, a higher-mobility carrier transport layer should be included in the D : A blend based device. However doing so will certainly result in a bilayer or even multilayer structure, which is usually a challenge for all-solution processing methods. Here by carefully controlling and adjusting the fabrication process, an all-solution-processed PBDTTT-CF/PBDTTT-CF : PCBM bilayer OTFP is demonstrated. In such a bilayer device, the PBDTTT-CF : PCBM blend layer is responsible for light absorption and free photo carrier generation, and the underlying PBDTTT-CF layer is responsible for the photo carrier transport inside the device. The hole mobility in the PBDTTT-CF layer is measured to be 9.1 × 10−4 cm2 V−1 s−1, much higher than that in the PBDTTT-CF : PCBM blend film, which is only 4.3 × 10−5 cm2 V−1 s−1. As a result of the faster carrier transport, the bilayer device exhibits a greatly enhanced photocurrent, which is about 7 times higher than that of the single blend layer device. Meanwhile, the on/off response of the bilayer device is also improved, which is shorter than 0.1/0.1 s.

All-solution-processed PIN architecture for ultra-sensitive and ultra-flexible organic thin film photodetectors

An ideal organic thin film photodetectors (OTFPs) should adopt a hierarchical, multilayer p-type/blend-type/n-type (PIN) structure, with each layer having a specific purpose which could greatly improve the exciton dissociation while guarantee efficient charge transport. However, for the traditional layer-by-layer solution fabrication procedure, the solvent used can induce organic material mixing and molecular disordering between each layer. Hence, such architecture for OTFPs can now only be formed via thermal evaporation. In this paper, a contact-film-transfer method is demonstrated to all-solution processing organic PIN OTFPs on flexible substrates. The fabricated PIN OTFPs exhibit high photoresponse and high stability under continuous mechanical bending. Hence, the method we described here should represent an important step in the development of OTFPs in the future.

Graphdiyne for multilevel flexible organic resistive random access memory devices

Graphdiyne (GD), a new carbon allotrope with a 2D structure comprising benzene rings and carbon–carbon triple bonds, is employed in fabricating resistive random access memory (RRAM) devices. On inserting a GD nanoparticle (NP) discontinuous layer and thermally depositing an Al–Al2O3 core–shell (Al–Al2O3) NP discontinuous layer in insulating polyimide (PI) films on a PET substrate, the designed flexible three-state memory device is realized (PET/Ag/PI/GD/PI/Al–Al2O3/PI/Al). GD NPs and Al–Al2O3 NPs function as two types of strong electron traps with different energy levels, resulting in two ON states. The OFF state and the two ON states possess long retention times of more than 104 s. Our results here demonstrate that GD could have great potential applications in future information storage technologies.