A Cathodoluminescence Study on the Diffusion Length in AlGaInP/InGaP/AlInP Solar Cell Heterostructures (original) (raw)
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IEEE Journal of Photovoltaics, 2021
We investigate the dynamics of Zn diffusion in MOVPE-grown AlGaInP/GaInP systems by the comparison of different structures that emulate the back-surface field (BSF) and base layers of a GaInP subcell integrated into an inverted multijunction solar cell structure. Through the analysis of secondary ion mass spectroscopy (SIMS), electrochemical capacitance-voltage (ECV) and spectrally resolved cathodoluminescence (CL) measurements, we provide experimental evidence that 1) the Zn diffusion is enhanced by point defects injected during the growth of the tunnel junction cathode layer; 2) the intensity of the process is determined by the cathode doping level and it happens for different cathode materials; 3) the mobile Zn is positively charged and 4) the diffusion mechanism reduces the CuPt ordering in GaInP. We demonstrate that using barrier layers the diffusion of point defects can be mitigated, so that they do not reach Zn-doped layers, preventing its diffusion. Finally, the impact of Zn diffusion on solar cells with different Zn-profiles is evaluated by comparing the electrical I-V curves at different concentrations. The results rule out the introduction of internal barriers in the BSF but illustrate how Zn diffusion under typical growth condition can reach the emitter and dramatically affect the series resistance, among other effects.
Effect of grain boundaries on the minority carrier diffusion length in InP solar cells
Solar Cells
A minority carrier diffusion length inhomogeneity induced by grain boundaries on indium tin oxide/CdS/InP and indium tin oxide/InP polycrystalline solar cells has been investigated. The open-circuit voltage method has been employed and scanning surface photovoltage measurements have been carried out. By illuminating selected areas of the devices with a light of low intensity whose energy was varied in a narrow spectral range above the energy band gap of InP, a decrease in the diffusion length corresponding to the grain boundary position was detected.
Applied Physics Letters, 1976
Lately a new luminescence based spatially resolved method to measure minority carrier diffusion lengths on Silicon Solar cells was introduced using Electroluminescence (EL) . The idea of this method is to analyze the reabsorption-shaped form of the emitted luminescence spectrum with optical filters, enabling one to determine the depth distribution of excess minority carriers which is directly related to diffusion length. This article is concerned with the extension of this method to Photoluminescence (PL), allowing for a diffusion length mapping in all stages of cell production. Problems associated with this method -such as filter inhomogeneities, fluorescence of filters, texturing, the nature of surface reflection and surface recombination -are addressed. Different PL measurement setups are discussed theoretically and with respect to measurement results. Diffusion length images measured with the technique are demonstrated.
Solar Energy Materials and Solar Cells, 2012
In this study, we demonstrated the fabrication and characterization of p-GaAs/i-InGaAsN/n-GaAs double hetero-junction solar cells (DHJSCs). The intrinsic InGaAsN absorption layer which is latticematched with GaAs substrates was grown by the metal-organic vapor phase epitaxy (MOVPE) system. The metal-organic sources used in the MOVPE growth induced unintentionally-doped carbon adatoms, and this in turn caused some carbon-related defects. This carbon pollution subsequently deteriorated the optical and electrical characteristics of the dilute nitride material. With ex-situ post-annealing being carried out in the furnace, it could not only modify the crystallinity of the InGaAsN material, but the deterioration in the performance of the dilute nitride solar cell due to the nitrogen incorporation could also be mitigated. After conducting the thermal annealing at 550 1C for 1 h in nitrogen ambience, the conversion efficiency of the DHJSCs was increased from 0.61% to 4.46% under Air Mass 1.5 Global (1000 W/m 2 , AM1.5 G) irradiance. The external quantum efficiency (EQE) spectrum further revealed that the efficiency of DHJSCs had been enhanced significantly owing to the crystalline improvement of the intrinsic InGaAsN absorption layer after the ex-situ post-thermal annealing was implemented. This improvement also led to a significant increase in the short-circuit current. The X-ray photoelectron spectroscopy (XPS) measurement result also showed that the ex-situ thermal annealing contributed to the improvement of crystal quality and the reduction of carbon related defects and clusters in the asgrown InGaAsN absorption layer.
IEEE Journal of Photovoltaics, 2017
The carrier recombination dynamics of In-GaP/InGaAsP quantum wells are reported for the first time. By studying the photoluminescence (PL) and time-resolved PL decay of InGaP/InGaAsP multiple-quantum-well(MQW) heterostructure samples, it is demonstrated that InGaP/InGaAsP MQWs have very low non-radiative recombination rate and high radiative efficiency compared to the control InGaP sample. Along with the analyses of PL emission spectrum and external quantum efficiencies, it suggests that this is due to small confinement potentials in the conduction band but high confinement potentials in the valence band. These results explain several features found in InGaP/InGaAsP MQW solar cells previously.
Low Growth Temperature MOCVD InGaP for Multi-junction Solar Cells
Energy Procedia, 2015
In view of the realization of high efficiency four-junction solar cells, InGaP layers, lattice matched to InGaAs, and (001) 6° off Ge substrate are grown by low pressure MOCVD at growth temperatures as low as 500 °C. The grown samples are undoped, ptype (doped by Zn) and n-type (doped by Te) materials with thickness around 1 μm. The ternary compound composition and structural properties are analysed by High Resolution X-Ray Diffraction and Transmission Electron Microscopy (TEM). Completely disordered InGaP layers are obtained with a target energy gap above 1.88 eV and a controlled Zn concentration around 10 17 cm-3. The interface properties are studied by High Resolution TEM. A nanometric scale waviness is observed at the interface between InGaP and InGaAs and it is correlated to the step bunching of the substrate offcut. In addition to this, HRTEM shows a 2-3 nanometer thin layer originated by atomic interdiffusion between the As-and the P-based compounds. The difference in composition of this interdiffusion layer is demonstrated by depth resolved Cathodoluminescence (CL), which reveals-approaching the InGaP/InGaAs interface, a blue shift of the InGaP related peak and the appearance of a new CL emission band ascribed to a quaternary InGaAsP compound.
A comparative study of p(+)n and n(+)p InP solar cells made by a closed ampoule diffusion
1991
The purpose was to demonstrate the possibility of fabricating thermally diffused p(+)n InP solar cells having high open-circuit voltage without sacrificing the short circuit current. The p(+)n junctions were formed by closed-ampoule diffusion of Cd through a 3 to 5 nm thick anodic or chemical phosphorus-rich oxide cap layer grown on n-InP:S Czochralski LEC grown substrates. For solar cells made
Journal of Applied Physics, 2003
Photoluminescence and high resolution x-ray diffraction ͑HRXRD͒ were used to follow the diffusion of a lattice matched InGaAs/InP heterostructure at various annealing temperatures. At 900°C no strain was observed by HRXRD and this indicated that the two sublattices in the sample diffused at an equal rate and only compositions on the tie line between the two initial compositions were formed. At lower annealing temperatures strain was observed in the wells and barriers, the signs of which changed during the annealing process. This is indicative of the diffusion rates of the two sublattices changing during the annealing process. It is suggested that these effects may be due to the presence of the miscibility gap in the InGaAsP system.
IEEE Transactions on Electron Devices, 1981
New methods are presented and illustrated that enable the accurate determination of the diffusion length of minority carriers in the narrow regions of a solar cell or a diode. Other methods now available are inaccurate for the desired case in which the width of the region is less than the diffusion length. Once the diffusion length is determined by the new methods, this result can be combined with measured dark I-V characteristics and with small-signal admittance characteristics to enable determination of the recombination currents in each quasineutral region of the cell-for example, in the emitter, low-doped base, and high-doped base regions of the BSF (back-surface-field) cell. This approach leads to values for the effective surface recombination velocity of the high-low junctiofl forming the back-surface field of BSF cells or the high-low emitter junction of HLE cells. These methods are also applicable for measuring the minority-carrier lifetime in thin epitaxial layers grown on substrates with opposite conductivity type.