Photoelectric determination of the series resistance of multijunction solar cells

A method for determining the series resistance R _s of multijunction solar cells is suggested and sub-stantiated. The method uses the presence of a maximum in the dependence of the efficiency on the sunlight concentration ratio ??(X) or in that of the operating voltage on the photogenerated current, V _m (J _g ). The study employs the concept that, in a limited but practically important range of photogenerated currents (up to the maximum ??), the series resistance can be represented by a fixed quantity that is linear and independent of J _g . It is analytically substantiated that this resistance can be found from the formula R _S = (E/J _g )_{?? = max}, where E = AkT/q and A and J _g are local values of the ideality factor and photogenerated current at the maximum ?? (or V _m ). It is shown that the value of R _s , determined by this method, is independent of the spectral composition of the incident light, which was experimentally confirmed in a study of the photovoltaic characteristics of triple-junction InGaP/GaAs/Ge solar cells. The method is suitable for both multi- and single-junction photoelectric converters.     

The dislocation origin and model of excess tunnel current in GaP p-n structures

An excess tunnel current in GaP epitaxial nondegenerate p-n junctions on GaP and Si substrates was studied. An important experimental result is that the slope of exponential current-voltage (I–V) characteristic (in lnI–V coordinates) is independent of the width of the space-charge region, i.e., on n-and p-region doping levels. This fact is unexplained by existing models. A dislocation shunt model based on multihop tunneling through a dislocation line, which may be considered as a chain of parabolic potential barriers, is proposed. The density of dislocations predicted by this model is in agreement with the transmission electron microscopy (TEM) observations.     

Anomalies in Photovoltaic Characteristics of Multijunction Solar Cells at Ultrahigh Solar Light Concentrations

Technical Physics Letters - An anomaly appearing in the photovoltaic characteristics of triple-junction GaInP/GaAs/Ge and of the corresponding double-junction GaInP/GaAs solar cells at...     

Counteracting the Photovoltaic Effect in the Top Intergenerator Part of GaInP/GaAs/Ge Solar Cells

Semiconductors - The “top” intergenerator part situated between the GaInP and GaAs subcells (electric power generators) is analyzed. The shape of the light current–voltage...     

Current flow and potential efficiency of solar cells based on GaAs and GaSb p-n junctions

Dependence of the efficiency of single-junction and multijunction solar cells on the mechanisms of current flow in photoactive p-n junctions, specifically on the form of the dark current-voltage characteristic J-V, has been studied. The resistanceless J-V _j characteristic (with the series resistance disregarded) of a multijunction solar cell has the same shape as the characteristic of a single-junction cell: both feature a set of exponential portions. This made it possible to develop a unified analytical method for calculating the efficiency of singlejunction and multijunction solar cells. The equation relating the efficiency to the photogenerated current at each portion of the J-V _j characteristic is derived. For p-n junctions in GaAs and GaSb, the following characteristics were measured: the dark J-V characteristic, the dependence of the open-circuit voltage on the illumination intensity P-V _OC, and the dependence of the luminescence intensity on the forward current L-J. Calculated dependences of potential efficiency (under idealized condition for equality to unity of external quantum yield) on the photogenerated current for single-junction GaAs and GaSb solar cells and a GaAs/GaSb tandem are plotted. The form of these dependences corresponds to the shape of J-V _j characteristics: there are the diffusion- and recombination-related portions; in some cases, the tunneling-trapping portion is also observed. At low degrees of concentration of solar radiation (C < 10), an appreciable contribution to photogenerated current is made by recombination component. It is an increase in this component in the case of irradiation with 6.78-MeV protons or 1-MeV electrons that brings about a decrease in the efficiency of conversion of unconcentrated solar radiation.     

Finding the Energy Gap of Ga1 –xInxAs p–n Junctions on a Metamorphic Buffer from the Photocurrent Spectrum

Technical Physics Letters - A relationship has been established between the energy gap width of GaInAs p–n homojunctions and the saturation current. For this purpose, a method was suggested...