Semitransparent photovoltaics are of interest for building integration and window coatings, though demonstrate an intrinsic tradeoff between transparency and absorption / efficiency. We propose alleviating this tradeoff using light management nanostructures which selectively scatter light based on incident wavelength and angle, allowing transmission of normally incident light for window visibility and absorption of light at elevated angles. Two structures of interest are proposed and described: metal nanorods which scatter light via their localized surface plasmon resonance properties, and arrays of subwavelength nanopores in a dielectric which demonstrate coherent multiple scattering. Both structures can potentially be patterned over large areas by electrochemical oxidation of aluminum into self assembled nanoporous anodized aluminum oxide (AAO) films.
A flexible large area lighting devices have been demonstrated by PDMS films. The (polydimethylsiloxane) PDMS films doped with organic/inorganic materials. The PDMS film is favorable due to its heat stability, good transparency, and flexibility. This study aimed to combine both organic and inorganic materials for flexible large area lighting applications. The architecture consists of blue LEDs coupled to a leaky waveguide that is covered with the PDMS film. The white light was generated with the poly (9, 9-dioctylfluorene-co-benzothiadiazole)F8BT blended into the PDMS slurry. Organic wavelength conversion materials were chosen owing to their ability to decompose in nature. The more conventional inorganic phosphors such as YAG are difficult to decompose and may present environmental issues which can bring concerns in many lighting applications. These flexible PDMS films had thicknesses of 100μm, 440μm, and 980μm. The resulting white light devices had color temperatures of 8944K, 4863K, and 4429K, respectively. In this study, we have also compared the performance of the organic versus conventional YAG phosphor embedded films.
We investigate the optical scattering properties of self-assembled nanoporous anodized aluminum oxide (AAO) films, and propose integrating AAO as a backscattering layer for light management in thin film photovoltaics. Angle selective scattering and direction of light to extreme, near-horizontal angles can enable new functionality for semitransparent PV window coatings, allowing improved absorption of direct sunlight without sacrificing transparency in the normal direction. Scattering to extreme angles can also be exploited to aid light trapping in thin epitaxial semiconductor absorbers, without texturing.
Indium gallium nitride (InGaN) semiconductor quantum dots are an attractive candidate for scalable room temperature quantum photonics applications owing to their large exciton binding energy and large oscillation strength. Previously, we reported single photon emission from site-controlled InGaN quantum dot structures. However, large homogeneous linewidth and significant non-radiative recombination were thought to be linked to the nearby surface charge centers. These charge centers can lead to spectral diffusion and excessive non-radiative recombinations at high temperature. In this work, ammonium sulfide passivation was investigated. Nitrogen vacancies were successfully passivated by ammonium sulfide ((NH4)2Sx) treatment, and the emission linewidth of a single quantum dot was reduced by 5 meV. Furthermore, the linewidth broadening with an increasing temperature was suppressed in the temperature range from 9 K to 95 K in this study. Satellite emission peak believed to be associated with the nitrogen vacancy was observed for un-passivated quantum dots. The satellite peak was 55 ~ 80 meV away from the main InGaN emission peak and was eliminated after sulfide passivation.
We proposed a compact variable all-optical buffer using slow-light in semiconductor nanostructures. We discuss the general design principle via dispersion engineering. The buffering effect is achieved by slowing down the optical signal using an external control light source to vary the dispersion characteristic of the medium via electromagnetically induced transparency effect. We demonstrate that the semiconductor quantum dot structures can be used as a slow-light medium. In such structure, the total buffering time is variable and controlled by an external pump laser. We present a theoretical investigation of the criteria for achieving slow light in semiconductor quantum dots. New pump scheme is proposed to overcome the sample nonuniformity. Finally, optical signal propagation through the semiconductor optical buffer is presented to demonstrate the feasibility for practical applications.