Oxidized Window Layer for Group III-V Solar Cells
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Solution Overview
Problem
Conventional Group III-V compound semiconductor solar cell devices face efficiency losses due to surface recombination of photo-generated carriers and absorption of higher energy photons by the window layer, which has a limited band gap and is difficult to lattice-match with GaAs substrates.
Innovation Solution
A wet oxidation process is used to form an oxidized window layer with a wider band gap, minimizing surface recombination and improving transparency for higher energy photons by passivating surface states and preventing carrier recombination at the surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the band gap of the window layer is increased to reduce surface recombination, then carrier recombination is minimized, but it becomes difficult to grow materials with band gap larger than 2.0 eV that are lattice matched to GaAs substrates
Solution Approach 1:
The patent applies local quality by using InAlP window layers with specific aluminum content (x=0.5-0.8) that provide the required high band gap (>2.2 eV) locally at the window layer position. The InAlP material system allows achieving the high band gap requirement while maintaining lattice compatibility through compositional control, enabling localized optimization without compromising overall device manufacturability.
Solution Approach 2:
The patent changes the material composition parameter of the window layer from conventional InAlP with x<0.5 to InAlP with x=0.5-0.8, which increases the band gap to greater than 2.2 eV. This parameter change achieves the desired electrical property (reduced surface recombination) while the InAlP material system maintains lattice matching capability with GaAs substrates, resolving the manufacturing difficulty.
2Device complexity
If a conventional window layer is used, then the device structure is simple, but the overall efficiency decreases due to absorption of fourth wavelength photons
Solution Approach 1:
The patent changes the band gap parameter of the window layer to greater than 2.2 eV through compositional control of InAlP materials. This parameter change enables the window layer to transmit photons in the fourth wavelength range (ultraviolet and far blue) that would otherwise be absorbed, thereby improving overall device efficiency while maintaining a relatively simple single-layer window structure without complex multi-layer designs.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The oxidized window layer enhances the transmission of higher energy photons, reducing surface recombination and increasing the efficiency of solar cell devices by allowing more light to reach the cell units, particularly in the ultraviolet region.
Implementation Method 1
A wet oxidation process is used to form an oxidized window layer with a wider band gap
Implementation Method 2
passivating surface states of the solar cell devices
Data Source
Figure 1
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Figure 2B
AI summary
The present application utilizes an oxidation process to fabricating a Group III- V compound semiconductor solar cell device. By the oxidation process, a window layer disposed on a cell unit is oxidized to enhance the efficiency of the solar cell device. The oxidized window has an increased band gap to minimize the surface recombination of electrons and holes. The oxidized window also improves transparency at the wavelengths that were absorbed in the conventional window layer.