In this paper, we present findings on micro-concentrator photovoltaic cells composed of lattice matched subcells grown on GaAs and InP substrates, which are stacked into single, four-terminal devices using micro-transfer printing. The design, modeling, growth, fabrication and assembly of the devices will be described, and potential interconnection schemes to achieve efficient, two-terminal strings of cells with flexible current and voltage outputs and resilience to defects is discussed.
KEYWORDS: Solar cells, Composites, Silicon, Monte Carlo methods, Concentrated solar cells, Brain-machine interfaces, Resistance, Reliability, Gallium arsenide, Glasses
One advantage of microconcentrator photovoltaics (μ-CPV) is the range of possible circuit connection arrangements. Large numbers of cells can be connected in combinations of series and parallel strings, which can provide a means to protect the module against performance loss due to cell failure, cell shading, and other variations in cell parameters that may arise during the fabrication and wiring processes. We introduce a model to evaluate the best strategy for optimizing module reliability through circuit layout using a combination of series and parallel connected cell strings. The model uses realistic solar cell device parameters in an electrical network simulation, coupled with a Monte Carlo method to introduce defects into the array with different probabilities. We use the model to optimize the layout of a μ-CPV panel designed to be integrated with the conventional 60-cell crystalline silicon panels for diffuse light capture to produce a hybrid direct/diffuse CPV product.
KEYWORDS: Silicon, Indium gallium phosphide, Monte Carlo methods, Solar cells, Solar energy, Resistance, Renewable energy, Tandem solar cells, Photovoltaics, Energy efficiency
Mechanically stacked tandem solar cells are a potential near-term solution for increasing the efficiency of photovoltaic modules. Practical implementation requires an interconnection approach that maximizes efficiency and minimizes complexity and cost. Connecting the top and bottom cells in a voltage-matched configuration allows two-terminal modules to be fabricated without altering the cell design or processing methods. Here, we experimentally demonstrate two-terminal voltage-matched GaInP2 / Si minimodules. The two-terminal minimodules performed just as well as four terminal configurations when voltage-matching requirements were met. The magnitude of the efficiency loss experienced by the voltage-matched minimodule when voltage-matched conditions were not met depends on whether the voltage was constrained by the GaInP2 or Si cells. Monte Carlo simulations also indicate that the two-terminal voltage-matched tandems respond to small cell-to-cell parameter variations in a similar manner as four terminal tandems.
KEYWORDS: Silicon, Indium gallium phosphide, Photovoltaics, Solar cells, Crystals, Temperature metrology, Tandem solar cells, Solar energy, Systems modeling, Electronics
This work examines a tandem module design with GaInP2 mechanically stacked on top of crystalline Si, using a detailed photovoltaic (PV) system model to simulate four-terminal (4T) unconstrained and two-terminal voltage-matched (2T VM) parallel architectures. Module-level power electronics is proposed for the 2T VM module design to enhance its performance over the breadth of temperatures experienced by a typical PV installation. Annual, hourly simulations of various scenarios indicate that this design can reduce annual energy losses to ∼0.5% relative to the 4T module configuration. Consideration is given to both performance and practical design for building or ground mount installations, emphasizing compatibility with existing standard Si modules.
A tunnel junction has been developed with an application to multijunction solar cells grown on GaSb and analyzed using a combination of electrical device measurements and modeling. The device employs an InAs quantum well embedded in a GaSb p/n junction, exploiting the high tunnel probability at the broken-gap interface between p-type GaSb and n-type InAs and having a minimal impact on the transparency of the device. The concept is extended to wider bandgap heterointerfaces using Al0.2Ga0.8Sb, achieving a differential resistance of 4.08×10−4 Ω cm2.
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