Using an appropriate SeS2/Se weight ratio, band gap grading was realized. By increasing the value of VOC through band gap grading in the depletion region, a record VOC deficit of 0.576 V and an efficiency of 12.3% were obtained.

Facile control over the morphology of phase pure tin monosulfide (SnS) thin films, a promising future absorber for thin film solar cells, is enabled by controlling the growth kinetics in vapor transport deposition of congruently evaporated SnS. The pressure during growth is found to be a key factor in modifying the final shape of the SnS grains. The optimized cube‐like SnS shows p‐type with the apparent carrier concentration of ≈1017 cm−3 with an optical bandgap of 1.32 eV. The dense and flat surface morphology of 1 µm thick SnS combined with the minimization of pinholes directly leads to improved diode quality and increased shunt resistance of the SnS/CdS heterojunction (cell area of 0.30 cm2). An open‐circuit voltage of up to 0.3068 V is achieved, which is independently characterized at the Korea Institute of Energy Research (KIER). Detailed high‐resolution transmission electron microscopy analysis confirms the absence of detrimental secondary phases such as Sn2S3 or SnS2 in the SnS grains or at intergrain boundaries. The initial efficiency level of 98.5% is maintained even after six months of storage in air, and the final efficiency of the champion SnS/CdS cell, certified at the KIER, is 2.938% with an open‐circuit voltage of 0.2912 V.

Micro-light emitting diode ͑LED͒ arrays with diameters of 4 to 20 m have been fabricated and were found to be much more efficient light emitters compared to their broad-area counterparts, with up to five times enhancement in optical power densities. The possible mechanisms responsible for the improvement in performance were investigated. Strain relaxation in the microstructures as measured by Raman spectroscopy was not observed, arguing against theories of an increase in internal quantum efficiency due to a reduction of the piezoelectric field put forward by other groups. Optical microscope images show intense light emission at the periphery of the devices, as a result of light scattering off the etched sidewalls. This increases the extraction efficiency relative to broad area devices and boosts the forward optical output. In addition, spectra of the forward emitted light reveal the presence of resonant cavity modes ͓whispering gallery ͑WG͒ modes in particular͔ which appear to play a role in enhancing the optical output.

For kesterite copper zinc tin sulfide/selenide (CZTSSe) solar cells to enter the market, in addition to efficiency improvements, the technological capability to produce flexible and large-area modules with homogeneous properties is necessary. Here, we report a greater than 10% efficiency for a cell area of approximately 0.5 cm 2 and a greater than 8% efficiency for a cell area larger than 2 cm 2 of certified flexible CZTSSe solar cells. By designing a thin and multi-layered precursor structure, the formation of defects and defect clusters, particularly tin-related donor defects, is controlled, and the open circuit voltage value is enhanced. Using statistical analysis, we verify that the cell-to-cell and within-cell uniformity characteristics are improved. This study reports the highest efficiency so far for flexible CZTSSe solar cells with small and large areas. These results also present methods for improving the efficiency and enlarging the cell area.

Matrix-addressable arrays of InGaN micro-lightemitting diodes with 128 96 pixels and a resolution of 1200 dpi have been fabricated using a novel "sloped sidewall" process. The devices have been fabricated on InGaN blue and green wafers, emitting light at the wavelengths of 468 and 508 nm, respectively. A simple circuit, which enables the display of an arrow pattern with 60% of the pixels turned on, was used for device testing. At an injection current of 60 mA, the devices deliver 3.3 (blue) and 2.4 mW (green) of output power, corresponding to a luminance of more than 30 000 Cd/m 2. These high-brightness and highly versatile devices are certainly an attractive form of emissive micro-display.

We report the fabrication of hybrid organic/inorganic semiconductor light-emitting devices that operate across the entire visible spectrum. The devices are based on a series of blue-, green-, and red-light-emitting polyfluorene materials that convert the emission from an array of micron-sized ultraviolet InGaN light-emitting diodes. We also demonstrate white-light-emitting versions of these hybrid devices by employing single films of carefully adjusted polyfluorene blends in which cascade energy transfer occurs between the constituent materials. The spectral and operating characteristics of the devices are described in detail. Such organic emission layer/inorganic light-emitting diode (LED) array based devices may provide a promising route to the fabrication of low-cost full-color microdisplays and other instrumentation devices.

We report on the fabrication of ultraviolet (UV) microarray light-emitting diodes, toward applications including mask-free photolithographic exposure. Devices with 64 64 elements have been fabricated in matrix-addressed format, generating directed output powers of up to 1 W per 20-m-diameter element at less than 1.0-mA drive current. The resistance of each elemental device was found to depend strongly on the n-GaN stripe length. The center wavelength of the emission was measured to be 368 nm, which is very close to that of an-line (365 nm) UV light source. To our knowledge, this is the first report detailing the fabrication and performance of such devices operating in the UV.

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