Under ultra-high solar concentration, an anomalous open-circuit voltage drop-out has been observed experimentally, but not understood theoretically. This anomaly is often attributed to various thermal effects but is also observed in flash testing, where thermal effects do not have time to accumulate. As the optically generated carrier density increases past the equilibrium carrier density, open-circuit voltage and other important electrical properties could deteriorate. Using Newton linearizations and the finite-element library deal.II, we developed a computational model to solve the carrier continuity equations for optically generated charge carriers as a function of material depth in bulk III-V semiconductors.

Split spectrum photovoltaics, where incident light is divided onto multiple cells on the basis of wavelength, are an exciting recent development in the solar energy field. This technology has the potential to exceed record conversion efficiencies by utilizing a large number of p-n junctions while mitigating the constraints that plague monolithic cells: lattice matching and current matching. Each cell in a split spectrum system can have a different lattice constant (allowing for more combinations of materials) and to have different operating currents (allowing for more combinations of band spacing).In this work, we examine a split spectrum system utilizing a single spectrum splitting device (a dichroic filter) to divide the solar spectrum onto two cells. Whereas many split spectrum designs use numerous filters to direct light onto single junction cells, in this system each cell is composed of multiple active junctions. Each cell is then tailored to absorb a portion of the solar spectrum. The combination of the two cells allows for four, five, or more active junctions while maintaining lattice and current matching conditions in each cell.A number of different cutoff frequencies for the dichroic filter are examined. Each cutoff frequency corresponds to its own combination of ideal band placements for both the shorter and longer wavelength cells. Materials corresponding to those band placements are examined to determine if any combinations can satisfy lattice matching parameters; designs which do are then simulated using TCAD Sentaurus.

We present gallium antimonide (GaSb) p–i–n photodiodes for use as thermophotovoltaic (TPV) cells grown on gallium arsenide (100) substrates using the interfacial misfit array method. Devices were grown using molecular beam epitaxy and fabricated using standard microfabrication processes. X-ray diffraction was used to measure the strain, and current–voltage (I–V) tests were performed to determine the photovoltaic properties of the TPV cells. Energy generation at low efficiencies was achieved, and device performance was critically analyzed.

The first decade of the 21st-century has seen a rapid development in infrared photodetector technology. At the end of the last millennium there were two dominant IR systems, InSb- and HgCdTe-based detectors, which were well developed and available in commercial systems. While these two systems saw improvements over the last twelve years, their change has not nearly been as marked as that of the quantum-based detectors (i.e., QWIPs, QDIPs, DWELL-IPs, and SLS-based photodetectors). In this paper, we review the progress made in all of these systems over the last decade plus, compare the relative merits of the systems as they stand now, and discuss where some of the leading research groups in these fields are going to take these technologies in the years to come.

Submitted for the MAR12 Meeting of The American Physical Society Efficiency Analysis and Demonstration of SplitJunction Photovoltaic Solar Cells HAN CHEN, EMIR MAGDEN, CHANDLER DOWNS, THOMAS VANDERVELDE, Tufts University — Recently, it has been proposed that separating solar radiation with a split-junction solar cell can result in higher overall conversion efficiencies, than are possible for monolithic designs. This hypothesis is investigated by simulating and analyzing 2+1 split junction cells for efficiency comparisons with theoretical and actual multi-junction cells. Ideal bandgaps for simultaneously operating photovoltaic and thermophotovoltaic cells have been determined. With the new configuration, it is shown that the efficiency achievements previously set by Ge/InGaAs/InGaP cells can be surpassed. A total increase in power output is observed during field tests using a Cassegrain split-junction concentrator with a dichroic lens (1.1 micron cutoff wavelength). Proposed benefits such as reduced heat load on the solar cell and ease of lattice constant matching in cell design are also validated. Additionally, with the flexibility of the concentrator assembly, it is shown that similar split-junction configurations with matching dichroic lenses allow for significant improvements in high efficiency solar cell technology. Emir Magden Tufts University Date submitted: 11 Nov 2011 Electronic form version 1.4