The external quantum efficiency (EQE) or associated spectral response is widely used to evaluate the performance of photovoltaics, light emitting diodes, photodetectors, photodiodes, semiconductor lasers, laser-induced refrigeration of solids etc. For photovoltaic (PV) devices, The EQE is used to determine the spectral mismatch correction that is used to convert a performance measurement from a non-ideal simulator spectrum to a standard spectrum in PV device calibrations. Moreover, EQE can provide important insight into the physics of a PV device. For instance, the EQE shape can be used to infer mechanisms limiting the performance of the device. However, EQE measurements of full-size PV modules remain a challenge in the PV community due to rare availability of reliable module QE measurement tools worldwide and the size and complexity of module architecture that comprises several cells connected in strings (series or/and parallel). Here, we use a customized nondestructive tool made of high-power light emitting diodes to perform high-throughput EQE measurements on PV modules. Circuit simulations show that the measurement system can safely be used to measure both crystalline silicon and thin film-based PV modules with series connected cells without the risk of damage through reverse bias. In addition, EQE mapping combined with electroluminescence show a strong correlation and provide a way to determine both spatial non-uniformity of the spectral response and defects/degradation effects across the module.
Optimizing a concentrator system which uses multijunction solar cells is challenging because: (a) the conditions are
variable, so the solar cells rarely operate under optimal conditions and (b) the conditions are not controlled, so any
design problems are difficult to characterize. Any change in the spectral content of direct-beam sunlight as it passes
through the concentrator optics is of particular interest, as it can reduce the performance of multijunction cells and is
difficult to characterize. Here we show how the fill factor can be used to detect and diagnose this sort of a "spectral
skewing" by the concentrator optics during outdoor operation. The work presented here is for GaInP2/GaAs tandem
cells, but the conclusions are equally valid for GaInP2/GaAs/Ge triple-junction cells.
Incorporation of a few percent of nitrogen into conventional III-V compounds to form III-N-V alloys such as GaNAs and GaNP leads to a large reduction of the fundamental band gap. We show experimentally and theoretically that the effect originates from an anti-crossing interaction between the extended conduction-band states and a narrow resonant band formed by localized N states. The interaction significantly alters the electronic band structure by splitting the conduction band into two nonparabolic subbands. The downward shift of the lower conduction subband edge is responsible for the N-induced reduction of the fundamental band-gap energy.
Conference Committee Involvement (6)
High and Low Concentrator Systems for Solar Energy Applications IX
19 August 2014 | San Diego, California, United States
High and Low Concentrator Systems for Solar Electric Applications VIII
27 August 2013 | San Diego, California, United States
High and Low Concentrator Systems for Solar Electric Applications VII
13 August 2012 | San Diego, California, United States
High and Low Concentrator Systems for Solar Electric Applications VI
23 August 2011 | San Diego, California, United States
High and Low Concentrator Systems for Solar Electric Applications V
3 August 2010 | San Diego, California, United States
High and Low Concentration for Solar Electric Applications
14 August 2006 | San Diego, California, United States
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