Versatile in-line Roll-to-roll Process for Flexible, Thin-Film Devices

Fabricating devices with non-vacuum roll-to-roll processes that intrinsically host nano-scale pn junctions offer an attractive platform to create low-cost, flexible, lightweight opto-electronic devices. Incumbent 3G nano technologies still face significant challenges in-terms of stability, toxicity, up-scaling and reproducibility to reach the status of the established technology. Here we present an alternate path that integrates new device structure, process and manufacturing. It features a compact, practical, atmospheric process to manufacture high quality, ordered 3D
nanocrystalline pn homojunction (NHJ) device structures. Exemplified here by two Cu-In-Se (CISe) compounds, the method entails single-step electrodeposition of interconnected network of p-CISe and n-CISe nanocrystals to create a depleted NHJ thin film. Extraordinary attributes the CISe NHJs include non-linear emissions, large carrier mobility, low trap-state-density, long carrier lifetime and likely up-conversion. The NHJ film can be inserted between two electrodes to produce an isotropic device, wherein current can flow in either direction to convert light into electricity or applied voltage into light.
Although originally conceived for CISe solar cells, this radical concept could create NHJs with most II-VI or III-V semiconductors for wide spectrum of applications, e.g., PV panels, LEDs, photodetectors, photoelectrodes, laser diodes, displays, MEMS and optical fibers. Importantly, the NHJ structure can be continuously roll-to-roll processed in ambient atmosphere from aqueous solution. Overall, this approach offers a promising low-cost processing platform to create high performance, stable and scalable devices. The NHJs could essentially perform like 2D planar pn
junctions or artificially ordered 3D nano-structures, but without their high cost and fabrication complexities.