G. Martínez-Denegri, J. Toudert, M. Kramarenko, S. Colodrero, Q. Liu, G. Kozyreff, J. Martorell
ICFO - Instituto de Ciencias Fotónicas,
Keywords: liquid crystal displays (LCD), light recycling, ergodic light propagation, polarization, perovskite solar cell
Summary:Liquid crystal display (LCD) is the most widely used technology to obtain high resolution full color images in current electronic devices. Unfortunately, such high quality images come with no consideration for any kind of energy management. Indeed, in current portable electronics or large TV monitor screens based on LCDs, 95% of the light emitted by the LEDs does not reach the eye of the user but instead it is lost as heat somewhere in the device. In here, we propose an innovative light guiding system, which we name half-Cylinder Photonic Plate (h-CPP), based on a periodic array of intercalated half-cylinders where light propagates transversally to the cylinder axis as opposed to the standard longitudinal propagation. When collimated light is incident into one of the half-cylinders at one edge of the plate, diffused light will exit from the top surface of the h-CPP with a largely disordered light intensity pattern. Such highly disordered pattern or diffuse light is precisely what is needed in LCD illumination. In addition, such pattern extends in the direction perpendicular to the cylinder axes, clearly indicating that light is also effectively trapped. In other words, in such h-CPP ergodicity is reached within an ordered structure. The lack of any structural disorder to achieve ergodicity makes it plausible to implement a h-CPP incorporating a top polarizer and a bottom perovskite solar cell. Such a device would have the potential to harvest a large portion of the light with the undesired polarization for the LCD and recycle it back to electricity. Applying a soft-lithography technique we fabricated a PDMS based flexible h-CPP. We deposited such h-CPPs on one side of a 1 mm thick fused quartz glass substrate while we fabricated a perovskite solar cell on the opposite side of that same substrate. After a photovoltaic characterization of a number of such devices being illuminated through the h-CPP, we confirmed that the short circuit current enhancement we measured could be ascribed to an ergodic light propagation in such h-CPP structure. The combination of ergodicity and current generation confirmed the potential that h-CPPs have to be used as the core element in light to electricity recycling devices. In summary, we propose an innovative light guiding scheme to comprehensively address the energy efficiency issue for most of the technology that incorporates illumination or light harvesting in it. Its implementation may change energy management in LCD-based portable devices, extending time between battery charges and dramatically reducing overall energy consumption.