Optical component designs for concentrating photovoltaic systems with three different multijunction solar cells (MJSCs) are optimized to yield maximum system efficiencies under standard test conditions, specifically uniform illumination. Optimization uses an integrated optoelectrical approach with ray tracing of the optical train to generate an irradiance profile for input to the cell’s distributed circuit model. These cells, a three-junction lattice-matched (3JLM) solar cell, a three-junction lattice-mismatched inverted metamorphic (3JIMM) solar cell, and a four-junction lattice-matched (4JLM) solar cell, were individually designed for maximum efficiency at 1000×. The optical train introduces losses, modifies the spectrum, and produces a spatially nonuniform profile across the cell. We decouple spectral modification from spatial nonuniformity to separately determine their individual impacts on system efficiencies, finding the optimal set of optical design parameters for each case. Spectral modification yields modest loss penalties (from 1.0% to 1.6%, relative to the MJSC), but the impact of nonuniformity is more significant and cell dependent, with relative loss penalties of 1.1%, 3.8%, and 2.3%, for 3JLM, 3JIMM, and 4JLM, respectively. While spectral modification does not significantly impact design parameters, spatial nonuniformity does, with absolute losses of 1% and 3.4% if 3JIMM and 4JLM cells are used in a 3JLM optimized system, respectively.
Concentrator photovoltaic (CPV) technology has come a long way, with multi-junction solar cell efficiencies now
reaching up to 44.4%. Front contact grid design, crucial for improving efficiency, is typically performed for uniform
illumination, but this does not account for the real world conditions of non-homogeneous irradiance distributions. In this
work, we aim to optimize finger spacing for a linear grid under non-uniform illumination by using Simulation Program
with Integrated Circuit Emphasis (SPICE) analysis. A two-dimensional distributed resistance model is used to simulate a
lattice matched, triple-junction solar cell whose design parameters are determined by curve-fitting current-voltage curves
from each sub-cell to a two-diode equivalent-circuit model. Cell efficiency is considered to be a unimodal function that
varies with finger spacing so a golden-section search optimization algorithm is used to determine the optimal spacing.
Various Gaussian profiles are used to simulate non-uniform illumination and their effects on device performance.
Designs based on optimal spacing for non-uniform illumination show an efficiency increase of more than 0.5% absolute
at concentrations greater than 500 suns.
High-brightness, inorganic light-emitting diodes (LEDs) have been successfully utilized for edge-lighting of large
displays for signage. Further interest in solid-state lighting technology has been fueled with the emergence of small
molecule and polymer-based organic light-emitting diodes (OLEDs). In this paper, edgelit inorganic LED-based displays
and state-of-the-art OLED-based displays are evaluated on the basis of electrical and photometric measurements. The
reference size for a signage system is assumed to be 600 mm x 600mm based on the industrial usage. With the
availability of high power light-emitting diodes, it is possible to develop edgelit signage systems of the standard size.
These displays possess an efficacy of 18 lm/W. Although, these displays are environmentally friendly and efficient, they
suffer from some inherent limitations. Homogeneity of displays, which is a prime requirement for illuminated signs, is
not accomplished. A standard deviation of 3.12 lux is observed between the illuminance values on the surface of the
display. In order to distribute light effectively, reflective gratings are employed. Reflective gratings aid in reducing the problem but fail to eliminate it. In addition, the overall cost of signage is increased by 50% with the use of these
This problem can be overcome by the use of a distributed source of light. Hence, the organic-LEDs are considered as a
possible contender. In this paper, we experimentally determine the feasibility of using OLEDs for signage applications
and compare their performance with inorganic LEDs. Passive matrix, small-molecule based, commercially available
OLEDs is used. Design techniques for implementation of displays using organic LEDs are also discussed. It is
determined that tiled displays based on organic LEDs possess better uniformity than the inorganic LED-based displays.
However, the currently available OLEDs have lower light-conversion efficiency and higher costs than the conventional,
inorganic LEDs. But, signage panels based on OLEDs can be made cheaper by avoiding the use of acrylic sheet and
reflective gratings. Moreover, the distributed light output and light weight of OLEDs and the potential to be built
inexpensively on flexible substrates can make OLEDs more beneficial for future signage applications than the inorganic
Organic light-emitting diodes (OLEDs) have been utilized successfully for various applications such as microdisplays in cell-phones and digital cameras. However, the application of OLEDs for large area signage displays has not yet been established. This paper presents novel design techniques for implementing OLEDs as light sources for signage application. The designs are examined on the basis of signage uniformity, cost and manufacturing complexity. Advantages and limitations of each design are described. It is determined that a trade-off is required to choose a design for implementation. After evaluation and comparison of the designs, the most optimal design is chosen and implemented. Measurement results with the optimal design are described.