N.J. Ekins-Daukes

Development of a new 550/spl times/ concentrator module with 3J cells - performance and reliability

The status of the development of a new concentrator module in Japan is discussed based on three arguments, performance, reliability and cost. The peak uncorrected efficiency for a 7,056 cm/sup 2/ 400/spl times/ module with 36 solar cells connected in series was 26.6 % was measured in house. The peak uncorrected efficiencies of the same type of the module with 6 solar cells connected in series and 1,176 cm/sup 2/ area measured by Fraunhofer ISE and NREL were 27.4 % and 24.8 % respectively. The peak uncorrected efficiency for a 550/spl times/ and 5,445 cm/sup 2/ module with 20 solar cells connected in series was 28.9 %. The temperature corrected efficiency under the best sunshine condition in Japan for the 550/spl times/ module was 31.5/spl plusmn/2%. For reliability, some new degradation modes inherent to high concentration III-V solar cell system are discussed and a 20 year lifetime under concentrated flux exposure proven. The fail-safe issues of the concentrated sunlight are also discussed. For cost, the overall scenario for the reduction of material cost is discussed.

Deep-level defects introduced by 1 MeV electron radiation in AlInGaP for multijunction space solar cells

Presented in this paper are 1 MeV electron irradiation effects on wide-band-gap (1.97 eV) (Al0.08Ga0.92)0.52In0.48P diodes and solar cells. The carrier removal rate estimated in p-AlInGaP with electron fluence is about 1cm−1, which is lower than that in InP and GaAs. From high-temperature deep-level transient spectroscopy measurements, a deep-level defect center such as majority-carrier (hole) trap H2 (Eν+0.90±0.05eV) was observed. The changes in carrier concentrations (Δp) and trap densities as a function of electron fluence were compared, and as a result the total introduction rate, 0.39cm−1, of majority-carrier trap centers (H1 and H2) is different from the carrier removal rate, 1cm−1, in p-AlInGaP. From the minority-carrier injection annealing (100mA∕cm2), the annealing activation energy of H2 defect is ΔE=0.60eV, which is likely to be associated with a vacancy-phosphorus Frenkel pair (Vp‐Pi). The recovery of defect concentration and carrier concentration in the irradiated p-AlInGaP by injection relat...

Comparison of efficiency measurements for a HCPV module with 3J cells in 3 sites

A new HCPV with 3J solar cells and new concentrator optics consisting in a dome-shaped Fresnel lens and a kaleidoscope homogenizer was presented in the last SCC2003. This paper summarizes the evaluation done by three independent organizations and a manufacturer. The peak uncorrected efficiency for a 7,056 cm/sup 2/ 400/spl times/ (geometrical concentration ratio) module with 36 solar cells connected in series was 26.6% was measured in house. The peak uncorrected efficiencies of the same type of the module with 6 solar cells connected in series and 1,176 cm/sup 2/ area measured by Fraunhofer ISE, NREL and Toyohashi University of Technology were 27.4%, 24.8% and 25.9% respectively. The peak uncorrected efficiency for a 550/spl times/ and 5,445 cm/sup 2/ module with 20 solar cells connected in series was 28.9% in house. The peak uncorrected efficiency of the 550/spl times/ (geometrical concentration ratio) module evaluated by Toyohashi University of Technology was 27.0 %. The temperature corrected efficiency under the best sunshine condition in Japan for the 550/spl times/ module was 31.5 /spl plusmn/ 1.7%.

Radiation Resistance of Wide Band Gap

The effects of 30 keV proton irradiation on n+/ p AlInGaP solar cells are presented here. As the proton fluence increases to more than 1×1010 cm-2, the maximum power Pmax of the cell decreases markedly due to the introduction of defects by proton irradiation. From the changes in minority-carrier diffusion length determined by quantum efficiency modeling as a function of fluence, the damage constant KL for p-AlInGaP was estimated to be about 5.0×10-5. This value is comparable to that observed from 3 MeV proton-irradiated p-InGaP whereas it is lower than that observed from 3 MeV proton-irradiated p-InGaAsP and p-InGaAs cells. The maximum power recovery of the cell was observed by minority-carrier-injection-enhanced annealing (1 A/cm2), and the annealing activation energy for 30 keV proton-irradiation-induced defects in p-AlInGaP was determined as ΔE = 0.42 eV.

n^{+}/ p

The recovery of defects introduced in n+/p AlInGaP solar cells under the 1 MeV electron/30keV proton irradiation by the minority-carrier injection-enhanced annealing is presented here. As a forward bias injection (100 mA/cm2) time increases, DLTS signal of H1 and H2 defects, which are introduced by the 1 MeV electron irradiation, decreases, indicating that they are annealed out due to nonradiative electron-hole recombination enhanced process. The activation energy DeltaE for the recovery of defect centers (H1 and H2) by the injection was 0.50 eV and 0.60 eV, respectively. Under the 30 keV proton irradiation, HP1 and HP2 defect centers were produced, and the annealing activation energy of AlInGaP solar cells obtained from the injection (1 A/cm2) was 0.42 eV

AlInGaP Solar Cell for High-Efficient Multijunction Space Solar Cells

Deep level transient spectroscopy (DLTS) is the best technique for monitoring and characterizing deep levels introduced intentionally or occurring naturally in semiconductor materials and complete devices. DLTS has the advantage over all the techniques used to-date in that it fulfils almost all the requirements for a complete characterization of a deep centre and their correlation with the device properties. In particular the method can determine the activation energy of a deep level, its capture cross-section and concentration and can distinguish between traps and recombination centers. In this invited paper we provide an overview of the extensive R&D work that has been carrier out by the authors on the identification of the recombination and compensator centers in Si and III-V compound materials for space solar cells. In addition, we present an overview of key problems that remain in the understanding of the role of the point defects and their correlation with the solar cell parameters

Minority-Carrier Injection-Enhanced Recovery of Radiation-Induced Defects in n+p AlInGaP Solar Cells

New broad DLTS peak signals in GaAsN solar cell, grown by chemical beam epitaxy, were obtained using the combination of optical-irradiation and conventional Deep Level Transient Spectroscopy (DLTS). Those broad peak signals cannot be detected by conventional DLTS method in the dark. The broad peak signals were overlapped with three deep level states at least and showed the increase of DLTS peak intensity. However, the other deep level state (EV+0.60eV) showed no significant change of DLTS peak signals in the dark and optical excitation. The condition of minority carrier injection by optical irradiation indicated that the mechanism of carrier capture and emission at some deep centers had been changed.

DLTS: A Promising Technique for the Identification of the Recombination and Compensator Centers in Solar Cell Materials

The fundamental efficiency of a photovoltaic device is ultimately constrained by the temperature difference between the sun and the PV device. An ideal Shockley-Queisser single junction solar cell shows both a rise in limiting efficiency and reduction in optimum band-gap energy as the cell temperature is reduced. In the case of a solar cell that is dominated by parasitic non-radiative recombination at room temperature, an improvement in efficiency is shown when, at low temperature, radiative recombination dominates over all non-radiative modes. This low temperature, radiatively limited regime is not suitable for photovoltaic power generation, but is proposed as a useful regime for demonstrating demanding 3rd Generation photovoltaic device concepts that are otherwise too ambitious to function efficiently at room temperature

Optical DLTS for the study of recombination centers in GaAsN grown by chemical beam epitaxy

Higher conversion efficiency has been predicted theoretically for InGaP/In0.16Ga0.84As/Ge lattice-mismatched triple junction solar cells owing to widening of the effective range of the solar spectrum than the conventional lattice-matched solar cells. The most serious problem in lattice-mismatched system is the large lattice mismatch (~1%) between In0.16Ga0.84As and Ge cells. The effect of a thermal cycle annealing (TCA) process which is expected to reduce the defect density in this system has been discussed from electrical and structural viewpoints. The minority carrier lifetime in In0.16Ga0.84As emitter layers were improved after TCA treatment from TR-PL measurement. EBIC measurements showed a reduction of the structural defect such as misfit dislocations due to the TCA process in In0.16Ga0.84As base layers. The misfit components observed in the base layers may have some influence through the emitter layers

Photovoltaic Device Operation at Low Temperature

An investigation of lattice mismatched p-InGaP and p-AlInGaP diodes and solar cell structures has been carried out after irradiation with 1 MeV electron and subsequently after annealing. The overall spectra of the hole traps both in InGaP and AlInGaP, observed by deep level transient spectroscopy (DLTS), is slightly different. However, electron spectra are significantly different in both types of samples. Apparent correlations between the recoveries of short-circuit current and quantum efficiency, and the annealing of the H1, H2, and H3 defects is observed both in AlInGaP and InGaP. Capacitance-voltage (C-V) profile results imply that other trap levels, which were not observed by DLTS must play a more important role in the carrier removal process.