Ming-Ju Yang

High‐energy and high‐fluence proton irradiation effects in silicon solar cells

We have examined proton irradiation damage in high‐energy (1–10 MeV) and high‐fluence (≳1013 cm−2) Si n+‐p‐p+ structure space solar cells. Radiation testing has revealed an anomalous increase in short‐circuit current Isc followed by an abrupt decrease and cell failure, induced by high‐fluence proton irradiation. We propose a model to explain these phenomena by expressing the change in carrier concentration p of the base region as a function of the proton fluence in addition to the well‐known model where the short‐circuit current is decreased by minority‐carrier lifetime reduction after irradiation. The reduction in carrier concentration due to majority‐carrier trapping by radiation‐induced defects has two effects. First, broadening of the depletion layer increases both the generation–recombination current and also the contribution of the photocurrent generated in this region to the total photocurrent. Second, the resistivity of the base layer is increased, resulting in the abrupt decrease in the short cir...

Type conversion in irradiated silicon diodes

We have observed conversion from p- to n-type of the base layer of n+\p\p+ silicon diodes irradiated with more than roughly 5×1016 cm−2 1 MeV electrons. Annealing for 15 min at 200 °C results in a recovery of p-type conduction in diodes in which type conversion had been induced. Solar cells which employ the same diode structure are severely degraded by irradiation with more than 1016 cm−2 1 MeV electrons and show only a weak infrared response after irradiation with 1017 cm−2 1 MeV electrons, consistent with the creation of an n+\n\p structure due to type conversion.

Analysis of Radiation Damage to Si Solar Cells under High-Fluence Electron Irradiation

Radiation testing of Si n+–p–p+ space solar cells has revealed an anomalous increase in short-circuit current I sc, followed by an abrupt decrease and cell failure, induced by high-fluence (>1016 cm-2) electron irradiation. A model which can be used to explain these phenomena by expressing the change in majority-carrier concentration p of the base region as a function of the electron fluence has been proposed in addition to the well-known model in which I sc is decreased due to minority-carrier lifetime reduction with irradiation. The reduction in p due to majority-carrier trapping by radiation-induced defects has two effects; one is broadening of the depletion layer which contributes to the increase in the generated photocurrent and that in the recombination-generation current in the depletion layer, and the second is an increase in the resistivity of the base layer resulting in an abrupt decrease of I sc and failure of the solar cells.

Analysis of impurity diffusion from tunnel diodes and optimization for operation in tandem cells

Abstract The tunnel diode has been applied as an interconnector in monolithic devices such as tandem solar cells. However, thermal degradation due to impurity diffusion is often observed due to growth at above about 600°C. In this study, the impurity diffusion from highly doped tunnel junctions after annealing has been analyzed, and it has been suggested that carbon has the advantage of a low diffusion coefficient as the p-type impurities. Furthermore, the thermally stable double hetero (DH) structure GaAs tunnel diodes which have been proposed in our previous work have been optimized. The thermal degradation is greatly suppressed by using a DH-structure which consists of a GaAs tunnel diode sandwiched between Al x Ga 1− x As layers, and as a result, a higher tunnel peak current density can be achieved by optimizing the impurity concentration and DH composition.

Radiation-resistance of InGaP solar cells

Irradiation effects of 1-MeV electrons in In/sub 0.5/Ga/sub 0.5/P (hereafter written as InGaP) space solar cells fabricated on GaAs substrates have been examined in comparison with those of GaAs and InP cells. Superior radiation-resistance of InGaP cells compared to GaAs cells has been found in terms of solar cell properties and minority-carrier diffusion length. Moreover, minority-carrier injection-enhanced annealing of radiation-induced defects in InP-related materials has also been observed.

Investigation of High-Efficiency InGaP/GaAs Tandem Solar Cells under Concentration Operation

The photovoltaic properties of InGaP/GaAs tandem solar cells under concentration have been investigated for concentration application. A high efficiency of 31.2% has been obtained for the InGaP/GaAs tandem solar cell under 5.1 suns of AM1.5 illumination. However, as the light intensity further increases, the efficiency is limited due to the reduction in the fill factor. The results show that not only very high peak current density, Jp, of the tunnel diode but also the valley current density, Jv, of the tunnel diode is necessary for high concentration. The efficiency predictions of the InGaP/GaAs tandem cell based on a numerical analysis suggest that a conversion efficiency of over 35% will be obtained at 500 suns if the series resistance of less than 0.001 Ω/cm2 is realized. Photocurrent mismatch between the top and bottom cells during high-temperature operation has also been analyzed for the design of concentrator cells.

Displacement damage analysis of single crystal 50 /spl mu/m thick silicon solar cells

The authors compare the effects of irradiation with various energies on the output characteristics of silicon solar cells by writing the particle fluence as a displacement damage dose. Using this method, the degradation to a given cell structure in any radiation environment can be estimated. In addition, they show that the evolution of cell parameters can be calculated quite accurately using PC-1D with consideration of only the combined effects of minority carrier lifetime reduction and carrier removal. As a result, the behavior of different cell structures can be estimated very quickly.

A 3 kW PV-thermal system for home use

A combined 3 kW PV-thermal system has been proposed for home use. Combining PV and thermal conversion makes this system economically efficient and competitive with traditional power supplies. GaAs and Si concentrator solar cells have been measured under concentration as a candidate for use in this system. InGaP/GaAs tandem solar cells designed for 1-sun operation have been examined under concentration. The potential use of GaInP/GaAs tandem solar cells has been analyzed for this application. The properties of the thermal transfer unit of this system has been evaluated including the cooling of the solar cell holder.

Microscopic analysis of carrier removal in heavily irradiated silicon solar cells

We compare the effects of 1 MeV electrons and 10 MeV protons on n+/p/p+ silicon diodes, after irradiation and subsequently after annealing. Although the effects of proton and electron irradiation upon device performance are coherent, the defect spectra which the different particles produce are slightly different. The origin of the dominant trap state cannot yet be identified conclusively.

Properties of GaAs/InGaAs quantum well solar cells under low concentration ratios

Multi-quantum well (MQW) GaAs/In/sub 0.19/Ga/sub 0.81/As solar cells have been measured under low concentration levels (1/spl sim/4 suns). An efficiency of 22% has been obtained at a ratio of 4 suns as opposed to 18% under 1 sun AM1.5 conditions. We explain the results in terms of an enhancement in minority-carrier lifetime under concentration. Even when the concentration ratio is low, the high-injection regime can be achieved since the carrier concentration in the intrinsic layer is very low. The existence of a high concentration of defects in the base layer has been observed by the DLTS analysis. Enhancement of the minority-carrier lifetime under concentration is thought to be due to recombination probability saturation of recombination centers with high-injection of minority carriers.