Yaokang Zhang

Full‐Solution Processed Flexible Organic Solar Cells Using Low‐Cost Printable Copper Electrodes

Full-solution-processed flexible organic solar cells (OSCs) are fabricated using low-cost and high-quality printable Cu electrodes, which achieve a power conversion efficiency as high as 2.77% and show remarkable stability upon 1000 bending cycles. This device performance is thought to be the best among all full-solution-processed OSCs reported in the literature using the same active materials. This printed Cu electrode is promising for application in roll-to-roll fabrication of flexible OSCs.

Bio-inspired chemical fabrication of stretchable transparent electrodes

Stretchable and transparent electrodes are fabricated by chemical deposition of metal thin films on natural veins of leaves at ambient conditions. These vein-based transparent electrodes show excellent electro-optical property (0.9 Ω sq(-1) at 83% T) even at 50% tensile strains, ideal for flexible and stretchable optoelectronic devices.

Photoreactive and Metal‐Platable Copolymer Inks for High‐Throughput, Room‐Temperature Printing of Flexible Metal Electrodes for Thin‐Film Electronics

Photoreactive and metal-platable copolymer inks are reported for the first time to allow high-throughput printing of high-performance flexible electrodes at room temperature. This new copolymer ink accommodates various types of printing technologies, such as soft lithography molding, screen printing, and inkjet printing. Electronic devices including resistors, sensors, solar cells, and thin-film transistors fabricated with these printed electrodes show excellent electrical performance and mechanical flexibility.

Versatile biomimetic haze films for efficiency enhancement of photovoltaic devices

A low-cost biomimetic haze film (BHF) is fabricated by one-step replica molding of the petal texture of yellow roses with polydimethylsiloxane (PDMS). The BHF possesses very high haze transmission (75%) and ultrahigh diffusion transmittance (97%), superior anti-reflection ability, remarkable enhancement of light absorption at small incidence angles, and superb resistance to strong acids. When attached on top of the glass side of photovoltaic cells, the BHF significantly elongates the photon pathway in the active layer and enhances the light harvesting of the solar devices. As a result, the power conversion efficiency of Si solar cells, organic solar cells (OSCs) and perovskite solar cells (PSCs) is respectively improved remarkably by 6.8%, 10% and 15%. In addition, >65% of the photocurrent is maintained even at an extremely small light incidence angle (10°), which equals more than 2.7 times the efficiency enhancement of the solar cell without the BHF.

Printed light-trapping nanorelief Cu electrodes for full-solution-processed flexible organic solar cells

Light-trapping nanorelief metal electrodes have been proven to be an effective approach to improve the absorption performance of flexible organic solar cells (FOSCs). These nanorelief electrodes have been made by conventional vacuum deposition techniques, which are difficult to integrate with roll-to-roll fabrication processes. To address this challenge, this paper reports, for the first time, the fabrication of highly conductive nanorelief Cu electrodes on the flexible substrates through solution printing and polymer-assisted metal deposition at room temperature in the air. FOSCs made with these printed nanorelief Cu electrodes possess not only much improved power conversion efficiency, by 13.5%, but also significant enhancement in flexibility when compared with those made with flat Cu electrodes. Because of the low material and fabrication cost, these printed nanorelief Cu electrodes show great promise in roll-to-roll fabrication of FOSCs in the future.

Interfacial engineering of printable bottom back metal electrodes for full-solution processed flexible organic solar cells

Printing of metal bottom back electrodes of flexible organic solar cells (FOSCs) at low temperature is of great significance to realize the full-solution fabrication technology. However, this has been difficult to achieve because often the interfacial properties of those printed electrodes, including conductivity, roughness, work function, optical and mechanical flexibility, cannot meet the device requirement at the same time. In this work, we fabricate printed Ag and Cu bottom back cathodes by a low-temperature solution technique named polymer-assisted metal deposition (PAMD) on flexible PET substrates. Branched polyethylenimine (PEI) and ZnO thin films are used as the interface modification layers (IMLs) of these cathodes. Detailed experimental studies on the electrical, mechanical, and morphological properties, and simulation study on the optical properties of these IMLs are carried out to understand and optimize the interface of printed cathodes. We demonstrate that the highest power conversion efficiency over 3.0% can be achieved from a full-solution processed OFSC with the device structure being PAMD-Ag/PEI/P3HT:PC61BM/PH1000. This device also acquires remarkable stability upon repeating bending tests.

Scanning Nanowelding Lithography for Rewritable One-Step Patterning of Sub-50 nm High-Aspect-Ratio Metal Nanostructures

The development of a new nanolithographic strategy, named scanning nanowelding lithography (SNWL), for the one-step fabrication of arbitrary high-aspect-ratio nanostructures of metal is reported in this study. Different from conventional pattern transfer and additive printing strategies which require subtraction or addition of materials, SNWL makes use of a sharp scanning tip to reshape metal thin films or existing nanostructures into desirable high-aspect-ratio patterns, through a cold-welding effect of metal at the nanoscale. As a consequence, SNWL can easily fabricate, in one step and at ambient conditions, sub-50 nm metal nanowalls with remarkable aspect ratio >5, which are found to be strong waveguide of light. More importantly, SNWL outweighs the existing strategies in terms of the unique ability to erase the as-made nanostructures and rewrite them into other shapes and orientations on-demand. Taking advantages of the serial and rewriting capabilities of SNWL, the smart information storage-erasure of Morse codes is demonstrated. SNWL is a promising method to construct arbitrary high-aspect-ratio nanostructure arrays that are highly desirable for biological, medical, optical, electronic, and information applications.