Whitney Gaynor

Smooth Nanowire/Polymer Composite Transparent Electrodes

IO N Transparent electrodes are critical components of thin-fi lm optoelectronic devices such as displays and thin-fi lm solar cells. Most high-performance transparent conducting fi lms in use today are composed of sputtered metal oxides. [ 1 , 2 ] These fi lms can have sheet resistances under 20 Ω − 1 with 90% transmission when deposited at a high temperature onto glass and resistances increasing to 40–200 Ω − 1 with the same transmission when deposited at lower temperatures onto plastic substrates. [ 2 , 3 ] Recent research has focused on replacing conductive metal oxides with alternative materials that can be deposited from solution and can reproduce the performance of metal oxides on glass on various substrates, including plastics. In addition, metal oxides are brittle, [ 4 , 5 ] and thus alternative transparent conductor technologies are also focusing on fl exibility and robustness to enable lightweight, fl exible solar cells and other thin fi lm devices. Strategies for non-vacuum deposition of transparent electrodes make use of materials other than metal oxides [ 6 ]

Fully Solution-Processed Inverted Polymer Solar Cells with Laminated Nanowire Electrodes

We demonstrate organic photovoltaic cells in which every layer is deposited by solution processing on opaque metal substrates, with efficiencies similar to those obtained in conventional device structures on transparent substrates. The device architecture is enabled by solution-processed, laminated silver nanowire films serving as the top transparent anode. The cells are based on the regioregular poly(3-hexylthiophene) and C(61) butyric acid methyl ester bulk heterojunction and reach an efficiency of 2.5% under 100 mW/cm(2) of AM 1.5G illumination. The metal substrates are adequate barriers to moisture and oxygen, in contrast to transparent plastics that have previously been used, giving rise to the possibility of roll-to-roll solution-processed solar cells that are packaged by lamination to glass substrates, combining the cost advantage of roll-to-roll processing with the barrier properties of glass and metal foil.

Color in the Corners: ITO‐Free White OLEDs with Angular Color Stability

High-efficiency white OLEDs fabricated on silver nanowire-based composite transparent electrodes show almost perfectly Lambertian emission and superior angular color stability, imparted by electrode light scattering. The OLED efficiencies are comparable to those fabricated using indium tin oxide. The transparent electrodes are fully solution-processable, thin-film compatible, and have a figure of merit suitable for large-area devices.

Fully solution-processed organic solar cells on metal foil substrates

We demonstrate fully solution-processed organic photovoltaic cells on metal foil substrates with power conversion efficiencies similar to those obtained in devices on transparent substrates. The cells are based on the regioregular poly- (3-hexylthiophene) and C61 butyric acid methyl ester bulk heterojunction system. The bottom electrode is a silver film whose workfunction is lowered by Cs2CO3 using spin-coating to serve as a cathode. The transparent top anode consists of a conductive polymer in combination with a solution-processed silver nanowire mesh that is laminated onto the devices. Each layer of the device, including the transparent electrode, is fabricated from solution, giving rise to the possibility of completely printed solar cells on low-cost substrates.

Transparent and tandem solar cells using solution-processed metal nanowire transparent electrodes

Tandem architectures in which multiple energy gaps are combined in a series-connected stack of solar cells are seen as a promising approach to increasing the power conversion efficiency of organic solar cells to commercially relevant values. Even higher efficiencies can be obtained if the photocurrent-matching requirement of such tandem cells is removed by the use of intermediate electrodes in multi-terminal multijunction cells. We demonstrate semi-transparent organic solar cells and multi-terminal multijunction organic photovoltaic cells using a laminated metal nanowire mesh as a low-cost, high-performance intermediate electrode that can be deposited using a lamination process without damaging the fragile organic layers. Photocurrent matching is not required in the multi-terminal architecture. With adequate material combinations, this cell architecture can be used to build organic solar cells with efficiencies ≫10%.