Xianyu Deng

Highly efficient inverted organic solar cells using amino acid modified indium tin oxide as cathode

In this paper, we report that highly efficient inverted organic solar cells were achieved by modifying the surface of indium tin oxide (ITO) using an amino acid, Serine (Ser). With the modification of the ITO surface, device efficiency was significantly enhanced from 0.63% to 4.17%, accompanied with an open circuit voltage (Voc) that was enhanced from 0.30 V to 0.55 V. Ultraviolet and X-ray photoelectron spectroscopy studies indicate that the work function reduction induced by the amino acid modification resulting in the decreased barrier height at the ITO/organic interface played a crucial role in the enhanced performances.

Environmentally friendly biomaterials as an interfacial layer for highly efficient and air-stable inverted organic solar cells

Appropriate interfacial modification plays an important role in the high performance of organic solar cells. We report that a transparent cathode of indium tin oxide (ITO) modified with an ultrathin layer of peptide, an environmentally friendly biomaterial, shows an obvious reduction in the work function. Investigation of the device exhibits that the power conversion efficiency (PCE) was significantly increased from 2.12% to 8.13% with the use of the peptide modification. The inverted device with the peptide-modified ITO as the cathode showed significantly longer time efficiency delay in air than conventional forward devices with an active metal as the cathode. Because peptides are biological materials that exist naturally in living things, the results provide an environmentally safe method to fabricate highly efficient and air-stable organic solar cells.

Highly Sensitive and Broadband Organic Photodetectors with Fast Speed Gain and Large Linear Dynamic Range at Low Forward Bias

Photodetectors with high photoelectronic gain generally require a high negative working voltage and a very low environment temperature. They also exhibit low response speed and narrow linear dynamic range (LDR). Here, an organic photodiode is demonstrated, which shows a large amount of photon to electron multiplication at room temperature with highest external quantum efficiency (EQE) from ultraviolet (UV) to near-infrared region of 5.02 × 103 % (29.55 A W-1 ) under a very low positive voltage of 1.0 V, accompanied with a fast response speed and a high LDR from 10-7 to 101 mW cm-2 . At a relatively high positive bias of 10 V, the EQE is up to 1.59 × 105 % (936.05 A W-1 ). Inversely, no gain is found at negative bias. The gain behavior is exactly similar to a bipolar phototransistor, which is attributed to the photoinduced release of accumulated carriers. The devices at a low voltage exhibit a normalized detectivity (D*) over 1014 Jones by actual measurements, which is about two or three order of magnitudes higher than that of the highest existing photodetectors. These pave a new way for realization of high sensitive detectors with fast response toward the single photon detection.

Effects of cathode modification using spin-coated lithium acetate on the performances of polymer bulk-heterojunction solar cells

In this report, we show that the performances of polymer bulk-heterojunction solar cells were improved by inserting thin films of lithium acetate layers between the active layer and the cathode using a spin-coating process. Comparing with the device without the cathode modification, significant enhancements of Voc (open circuit voltage) from 0.42 V to 0.55 V and device efficiency from 1.4% to 4.1% were achieved. X-ray and ultraviolet photoelectron spectroscopic studies indicate that both the improved damage tolerance of the active layer under the thermally evaporated metal and an n-type doping at the metal/organic interface play the crucial roles in the enhanced performances.

Effects of Organic Cation Additives on the Fast Growth of Perovskite Thin Films for Efficient Planar Heterojunction Solar Cells

The film quality of organometallic halide perovskite is very crucial to the performance of planar heterojunction solar cells. Previous methods have generally required a long-time and complex process to control the crystal growth for obtaining a compact and smooth perovskite film. Here, we demonstrate a novel method of growing the high-quality films via a simple and rapid process. Organic cations are used as additives in the solution of CH3NH3PbI3 (MAPbI3), which plays a key role in the film-forming process. These organic cations can enhance the film-forming ability and do not lead to a residue in the film end-product. On the basis of these characteristics, highly efficient perovskite solar cells with a simple planar heterojunction structure were achieved. Because the additives can simplify and accelerate the fabrication process and have no chance to induce any negative effect on the device, they will have a large potential in the production of various high-quality perovskite films and low-cost, large-scale, and high-performance devices.

Biomaterial functionalized graphene oxides with tunable work function for high sensitive organic photodetectors

Graphene acts as an ideal material for transparent conductive electrodes in optoelectronic devices attributed to its excellent electrical conductivity, optical transparency, and mechanical properties. Graphene oxide (GO) in the form of a colloidal suspension is considered to be more commonly useful because of its low cost and high volume production. However, controlling the work function of graphene and GO as transparent electrodes in optoelectronic devices is still a challenging task, since it is important to match the energy level of the active materials. In this study, GO sheets functionalized with amino acids were fabricated via a mild and environmentally friendly approach. The work functions of the novel amino acid functionalized graphenes and their compounds with poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) were tuned over a wide range, which matched well with the energy of various semiconductors. Organic photodetectors with the functionalized GO exhibited the highest normalized detectivity of 5.7 × 1012 jones at −0.1 V. The results indicated that the synthesized solution-processable GO exhibits promising potential as transparent electrodes for various photoelectric devices.

New application of AIEgens realized in photodetectors: reduced work function of transparent electrodes and much improved performance

Highly sensitive organic photodetectors were achieved by tuning the work function of transparent electrodes using two AIEgens with different ionic side chains. With the insertion of AIE molecules, their projected detectivity (D*) was enhanced by over one order of magnitude, which was accompanied by a fast response speed and a large linear dynamic range. The devices exhibited the ability to effectively detect weak light with intensity less than 10 pW cm−2, which is clearly superior to traditional silicon photodetectors. The AIE molecules developed a good energetic match to facilitate photocurrents, and the non-conjugated ionic impeding effect blocked the electrons from transferring to the interface under dark conditions and lower dark currents, which significantly contributed to the high detectivity of the devices. This study indicates that high performance organic devices could be achieved by jointly controlling conjugation associated aggregation and the quantity and state of ions on the electrode surface, thus providing a new application for AIEgens.

Metal-Organic-Compound-Modified MoS2 with Enhanced Solubility for High-Performance Perovskite Solar Cells

MoS2 as a graphene-like 2 D material shows a large potential to replace and even overcome graphene in various important applications owing to its ideal properties of electrical, optical, frictional, and tunable band gap. However, its low solubility in the most of common solvents makes it difficult to prepare by a simple solution process. Here, we introduce a metal-organic compound to modify MoS2 . Phenyl acetylene silver (PAS)-functionalized MoS2 is easily dispersed in solvents like DMF and water. A conductive polymer PEDOT:PSS (poly(3,4-ethylenedioxythiophene) polystyrene sulfonate) blend with the MoS2 leads to a significant enhancement of the performance of planar heterojunction perovskite solar cells. The solar cells have a high power conversion efficiency of 16.47 % as well as largely increased stability. This provides a feasible method for large-scale production of MoS2 for wide applications in various electric devices.

Largely enhanced VOC and stability in perovskite solar cells with modified energy match by coupled 2D interlayers

Due to the use of a low-temperature solution process and the absence of hysteresis, PEDOT:PSS based p–i–n perovskite solar cells (PVSCs) have some obvious advantages, such as simple device technology, suitability for flexible and large size substrates, and long-term stability. However, so far their power conversion efficiency (PCE) has been much lower than that of other types of PVSCs, and in particular, they have a much lower open-circuit voltage (VOC). In this research, PEDOT:PSS based PVSCs achieve a large enhancement of VOC, PCE and device stability by using 2D materials like graphene oxide (GO) and MoS2 as interfacial layers. The CH3NH3PbI3 based PVSC with the GO and MoS2 layers shows an increased VOC from 0.962 to 1.135 V and an enhanced PCE from 14.15% to 19.14%. When a Br-doped perovskite of CH3NH3PbI2.5Br0.5 is used as the active layer, the VOC is enhanced from 1.010 to 1.176 V. The modified energy match at electrode interfaces plays a key role in the enhancement of device performance. This work indicates that 2D materials are important materials for use in interfaces of perovskite solar cells to largely enhance device performance and stability.

Full color polymer light-emitting diodes with photo-patterning process

Full-color polymer light-emitting diode (PLED) arrays presently are mainly produced by ink-jet printing. Here, we report a new approach for fabricating full-color PLED arrays that takes advantage of the low-cost and high throughput spin-coating and photo-patterning processes. Compared to previous approaches that also employed photo-patterning, our approach does not require wet processing steps, and the spectra of the colors emitted are not sensitive to the photopatterning time. Because the photo-pattering is a traditional technology which was proved to be successfully used in producing liquid crystal displays and other electrical productions, this method may provide a low-cost and high throughput procedure to manufacture polymeric flat-panel display devices.