High-efficiency multijunction or tandem solar cells based on group III–V semiconductor alloys are applied in a rapidly expanding range of space and terrestrial programs. Resistance to high-energy radiation damage is an essential feature of such cells as they power most satellites, including those used for communications, defense, and scientific research. Recently we have shown that the energy gap of In1−xGaxN alloys potentially can be continuously varied from 0.7 to 3.4 eV, providing a full-solar-spectrum material system for multijunction solar cells. We find that the optical and electronic properties of these alloys exhibit a much higher resistance to high-energy (2 MeV) proton irradiation than the standard currently used photovoltaic materials such as GaAs and GaInP, and therefore offer great potential for radiation-hard high-efficiency solar cells for space applications. The observed insensitivity of the semiconductor characteristics to the radiation damage is explained by the location of the band edge...

Superior radiation resistance of In1-xGaxN alloys: Full-solar-spectrum photovoltaic material system

III–V compound multi-junction solar cells: present and future

Effect of soiling on photovoltaic modules

Radiation-resistant solar cells for space use

A review of radiation-induced displacement damage effects in semiconductor devices is presented, with emphasis placed on silicon technology. The history of displacement damage studies is summarized, and damage production mechanisms are discussed. Properties of defect clusters and isolated defects are addressed. Displacement damage effects in materials and devices are considered, including effects produced in silicon particle detectors, visible imaging arrays, and solar cells. Additional topics examined include NIEL scaling, carrier concentration changes, random telegraph signals, radiation hardness assurance, and simulation methods for displacement damage. Areas needing further study are noted.

Displacement Damage Effects in Irradiated Semiconductor Devices

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 circuit current and failure of the solar cells.

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

An anomalous increase in the short‐circuit current Isc of n‐on‐p Si space solar cells, followed by an abrupt decrease in Isc and cell failure has been observed under high fluence (≳1016 cm −2) 1 MeV electron irradiation. A model to explain these phenomena by expressing the change in carrier concentration p, of the base region as a function of the electron fluence is proposed in addition to the well‐known model where Isc decreases by minority‐carrier lifetime reduction under irradiation. The reduction in p due to majority‐carrier trapping by radiation‐induced defects has two effects: broadening of the depletion layer which increases the generated photocurrent, and also an increase in the resistivity of the base layer, resulting in the abrupt decrease of Isc and failure of the solar cells.

Mechanism for the anomalous degradation of Si solar cells induced by high fluence 1 MeV electron irradiation

The observation of minority-carrier injection-enhanced annealing of radiation damage to InGa0.5P0.5/GaAs tandem solar cells is reported. Radiation resistance of InGaP/GaAs tandem solar cells as is similar with GaAs-on-Ge cells have been confirmed with 1 MeV electron irradiations. Moreover, minority-carrier injection under light illumination and forward bias conditions is shown to enhance defect annealing in InGaP and to result in the recovery of InGaP/GaAs tandem solar cell properties. These results suggest that the InGaP/GaAs(/Ge) multijunction solar cells and InGaP-based devices have great potential for space applications.

Superior radiation-resistant properties of InGaP/GaAs tandem solar cells

An accurate radiation degradation model, based on measured radiation damage to devices and physical principles on radiation-induced defects in Si, has been established to improve the radiation-resistance of the Czochralski (CZ)-grown and floating-zone (FZ)-grown single-crystal Si space solar cells. We have successfully carried out the optimization of radiation-resistant Si space solar cells by taking into account the effective base carrier concentration dependence of the most important analytical parameters, damage coefficient K/sub L/, for the minority-carrier diffusion length and carrier removal rate R/sub c/ for majority-carriers. The model can be used to adequately predict the radiation degradation of the Si solar cells irradiated with a complete spectrum of electron fluence. It has been established that the radiation-resistance of the silicon solar cell is very dependent on effective carrier concentration in the high fluence range and irradiation tolerance can be improved further by varying the base carrier concentration upon irradiation.

A detailed model to improve the radiation-resistance of Si space solar cells

The observation of minority-carrier injection-enhanced annealing of radiation-induced defects in InGaP is reported. 1-MeV electron irradiation results demonstrate superior radiation-resistance of InGa0.5P0.5 solar cells compared to GaAs-on-Ge cells. Moreover, minority-carrier injection under forward bias conditions is shown to enhance defect annealing in InGaP and to result in the recovery of InGaP solar cell properties. These results suggest that the radiation-resistance of InGaP-based devices such as InGaP/GaAs(/Ge) multijunction solar cells and InGaP(As) light-emitting devices is further improved under minority-carrier injection condition.

Stephen J. Taylor

Papers

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

Mechanism for the anomalous degradation of Si solar cells induced by high fluence 1 MeV electron irradiation

Superior radiation-resistant properties of InGaP/GaAs tandem solar cells

A detailed model to improve the radiation-resistance of Si space solar cells

Minority-carrier injection-enhanced annealing of radiation damage to InGaP solar cells