GaAs Solar Cell Back Surface Field for Low-Temperature Efficiency
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Standard solar cells experience significant performance losses at low temperatures, which is a challenge for applications operating below −50° C, such as UAVs and deep space exploration, as they are optimized for near room temperature performance.
Innovation Solution
A solar cell design featuring a gallium arsenide or indium gallium arsenide cell with a back surface field made of aluminum gallium arsenide or indium aluminum gallium arsenide, p-type doped with zinc or carbon, which forms a heterojunction with a lower barrier height, reducing resistive losses and maintaining efficiency at temperatures below −50° C.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If standard solar cells optimized for near room temperature performance are used, then performance at room temperature is good, but performance at low temperatures below −50° C. deteriorates significantly
Solution Approach 1:
The patent modifies the bandgap parameters of the solar cell materials to optimize performance at low temperatures. By selecting materials with appropriate bandgaps (GaAs, InGaAs, AlGaAs, InAlGaAs) and adjusting their compositional parameters, the cell maintains high quantum efficiency and reduces thermalization losses at temperatures below −50° C., resolving the contradiction between room temperature optimization and low temperature performance.
Solution Approach 2:
The patent employs a composite multi-junction structure combining different semiconductor materials (GaAs, InGaAs, AlGaAs, InAlGaAs) with complementary bandgaps. This composite approach allows the solar cell to capture a broader spectrum of sunlight while maintaining high efficiency at low temperatures, as each material layer contributes to overall performance without the limitations of single-material designs.
2Reliability
If a back surface field with high barrier height is used, then carrier separation is improved, but resistive losses increase at low temperatures
Solution Approach 1:
The patent applies local quality optimization by creating a back surface field with spatially varying doping profiles and material compositions. The AlGaAs or InAlGaAs layer is positioned at the back surface with specific doping concentrations that create an electric field localized at the interface, improving carrier separation where needed while minimizing resistive losses in the bulk material at low temperatures.
Solution Approach 2:
The patent adjusts the barrier height parameter of the back surface field to an optimal value that balances carrier separation and resistive losses. By controlling the aluminum composition ratio (x < 0.8) and doping levels in the AlGaAs or InAlGaAs layer, the barrier height is tuned to provide sufficient carrier separation while maintaining low series resistance at operating temperatures below −50° C.
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 new solar cell design achieves a 25% increase in efficiency at −150° C compared to baseline designs, with performance improving monotonically with decreasing temperature, and exhibits well-behaved light-current-voltage curves down to −150° C, significantly outperforming standard cells in low-temperature conditions.
Implementation Method 1
The barrier height allows for thermalization of majority carrier holes down to temperatures less than about −50° C., which eliminates resistive losses associated with the barrier.
Implementation Method 2
The back surface field may form a heterojunction with a middle cell (MC) base having a lower barrier height as compared to a middle cell back surface field comprised of gallium indium phosphide (GaInP).
Implementation Method 3
a solar cell having a cell comprised of gallium arsenide (GaAs) or indium gallium arsenide (InGaAs) with a back surface field (BSF) comprised of aluminum gallium arsenide (AlGaAs) or indium aluminum gallium arsenide (InAlGaAs)
Implementation Method 4
the back surface field acts as a hetero-step passivation layer and reflects minority carrier electrons back to a p-n junction to be collected
Data Source
AI summary
A solar cell having a cell comprised of gallium arsenide (GaAs) or indium gallium arsenide (InGaAs) with a back surface field (B S F) comprised of aluminum gallium arsenide (AlGaAs) or indium aluminum gallium arsenide (InAlGaAs) p-type doped for enhanced operation of the solar cell at temperatures less than −50° C. In one example, the back surface field comprises AlxGa1-xAs or In0.01AlxGa1-xAs, wherein x is less than about 0.8, for example, 0.2. The back surface field may be p-type doped with zinc (Zn) or carbon (C).