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Heterojunction emitter InAs/GaAs quantum dot solar cells (QDSC) with an In0.48Ga0.52P (InGaP) n-type emitter and p-type GaAs base were fabricated along with homojunction nip solar cells in order to enable sub-cell polarity compatibility of InAs/GaAs QDSCs with current state-of-the-art monolithic InGaP/GaAs/Ge triple junction solar cells for space applications and to investigate potential dark current suppression effects and electronic field enhancement effects on carrier collection in InAs/GaAs QDSC. Quantum dot solar cells with one-Sun AM0 open circuit voltages greater than 970 mV were fabricated as compared to a 1.020 V heterojunction emitter ‘control’ sample. Preliminary testing showed a reduction in short circuit current density from homojunction to heterojunction GaAs solar cells, primarily from changes in reflection and uncollected absorption in the InGaP emitter. [ABSTRACT FROM PUBLISHER]

The use of nanostructures, such as quantum dots (QD) or quantum wells within photovoltaic (PV) devices has demonstrated enhanced current generation, but often at the expense of open-circuit voltage. QD morphology and optical quality have a direct impact on PV performance and optimizing the epitaxial growth of QDs is critical to achieve the desired benefits of QD-enhanced PV. The spatial uniformity of QD epitaxy can determine the PV performance across a large area wafer. In this paper, we demonstrate a correlation between the spatial uniformity of QD size distribution and photovoltaic conversion efficiency. A spatially varying Voc measured on QD-enhanced GaAs solar cells correlates with the presence of coalesced QDs. The results suggest the presence of large, coalesced QDs is a significant cause for a reduced Voc in QD-enhanced GaAs p-i-n solar cells. [ABSTRACT FROM PUBLISHER]

The low temperature operation of GaAs solar cells incorporating a superlattice of InAs quantum dots (QD) was studied to explore carrier removal mechanisms. Dark current-voltage characteristics of QD devices did not show a temperature dependence, which suggests a tunneling-dominated recombination mechanism. Two-photon extraction was investigated using a pump-probe method, but no evidence of two-photon was observed. Finally, 1-sun measurements revealed a resonant-tunneling contribution to the current in the QD devices, which became prominent as temperature was reduced. [ABSTRACT FROM PUBLISHER]

Control of InAs critical thickness (θ) is important to realizing optimized growth in quantum dot (QD) devices. Substrate misorientation can change the value of θc but also creates more uniform QDs in both size and distribution. This work explores GaAs p-i-n photovoltaic (PV) devices grown via organometallic vapor phase epitaxy (OMVPE) using the Stranski-Krastanov (SK) growth method on substrates misoriented 6° off (100) in the [110] direction and 2°off (100) in the [110] direction. Test structures and single junction solar cells were grown in order to study device performance through light I-V measurements and spectral responsivity (SR) as well as material properties through atomic force microcopy (AFM) and photoluminescence (PL). Results of this work show that 2° [110] sample results in lower θc as compared to the 6° [110] (approximately 1.8 ML verses approximately 2.1 ML). The 6° [110] substrate also showed a more uniform density and size distribution of QDs. These results are important to realizing the full benefits of QD structures such as increased optical absorption. [ABSTRACT FROM PUBLISHER]

Results from ongoing development of spatial and spectral quality of RIT's dual source solar simulator are presented. This simulator as designed qualifies as class A for both AM0 and AM1.5, depending on the filter set used. Measurements were made of spatial intensity uniformity, as well as spectral uniformity across the 300 mm diameter beam under calibrated AM0 conditions. The beam exhibits intensity non-uniformity across the 300 mm diameter test plane of 5.89%, though typically cells can be measured in a 10 cm × 10 cm central region of 1.13% non-uniformity. Spectral match and spectral mismatch values were calculated for specific spectral regions and device structures, respectively, which verified a close match to both AM0 and AM1.5G, especially in the region most commonly used for triple junction solar cells. Results of a set of ten Emcore BTJs measured at Emcore, Aerospace Corporation, NASA Glenn Research Center, and RIT, were compared. It was found that RIT's simulator produced figures of merit such as VOC, ISC, fill factor, and efficiency, for these cells to within 2% of the other facilities. [ABSTRACT FROM PUBLISHER]

InAs quantum dots have been incorporated into the middle junction of an InGaP/(In)GaAs/Ge triple junction solar cell (TJSC) on four inch wafers, in aims of band gap engineering a high efficiency solar cell to even higher limits. Results of QD growth on 4” diameter Ge templates gave densities near 1×1011 cm−3 and QD height between 2–5 nm. Arrays of 10 layers of InAs QDs have been grown between the base and emitter in the middle cell of a full triple junction solar cell. Control triple junction cells that received growth interrupts without QD growth showed similar results (within 5 mV open circuit voltage) to standard triple junction cells without an interrupt. Integrated current of the (In)GaAs junction with 10 layers of strain balanced InAs QD layers shows a gain of 0.37 mA/cm2 beyond the band edge. One sun AM0 current-voltage measurements of QD TJSC show an efficiency of 26.9% with a Voc of 2.57 V. [ABSTRACT FROM PUBLISHER]