In this work, InGa.N-based multijunction solar cells are theoretically designed for high efficiency and the performance of the designed solar cells is evaluated with different parameters. The 1 band gap energies of the In.Ga1 N alloy system cover the entire air-5 mass-1.5 solar spectrum.
Background Information
To overcome these difficulties and increase the efficiency of the solar cell multijunction (MJ) approach, the multijunction (MJ) approach to solar cells is being used all over the world. Photovoltaic concentrator systems using high efficiency solar cells are one of the important issues in the development of an advanced PV system.
Purpose of Research
More work on the theoretical design and performance evaluation of InGa1N-based MJ solar cells for high efficiency is urgently required. Unless specified, the estimated performance shown in this thesis is for InGa1 N-based MJ solar cells of n in p-type cells.
Thesis Organization
In order to compete with a greater cost reduction of MJ solar cells, the concentrators are designed for high-efficiency photovoltaic systems. It proposed the multi-sun approach for future work to be done to achieve better performance of solar cells.
Introduction
Working Principle of Solar cell
Consequently, an open-circuit voltage develops between the terminals of the device with the p-side positive with respect to the n-side. Those photogenerated holes within a diffusion length L can reach the depletion layer and be swept over to the p-side.
Efficiency Losses of Solar Cell
- Reflection Losses on the Surface
- Incomplete Absorption
- Utilization of Only Part of the Photon Energy to Create EHPs
- Incomplete Collection of EHPs
- Voltage Factor V.F
- Fill Factor or Curve Factor Loss
- Recombination before Drift
- Series and Shunt Resistance
- Top Surface Contact Obstruction
The fill factor (FF) is a measure of the junction quality and series resistance of the cell. The series resistance of the cell can cause deviation from the ideal voltage-current characteristics.
Approaches to Increase Efficiency
- Multiple Junction Solar Cells
- Multiple Spectrum Solar Cells
- Multiple Absorption Path Solar Cells
- Multiple Energy Level Solar Cells
- Multiple Temperature Solar Cells
This technology can be applied to any solar cell provided power obtained by spectral alternation offsets the cost of the additional optical coating. Since many of the proposed approaches can potentially be implemented in a low-cost manner, multiple spectrum solar cells primarily provide a mechanism for relatively modest efficiency increases using existing solar cell technology. A central limitation of existing solar cell ap1roaches is the one-to-one relationship between an absorbed photo1 and a generated electron-hole pair.
In solar cells with multiple energy levels, the mismatch between the incident energy of the solar spectrum and a single band gap is adjusted by introducing additional energy levels so that photons of different energies can be efficiently absorbed. The multiple temperatures may be due to variations in the physical temperature of the grid, but it is easier to maintain a temperature difference between hot carriers and thermalized carriers.
Multijunction: An Exciting Approach to High Efficiency
V0ç and conversion efficiency, 11, of the InGa3 N-based MJ solar cells with the surface recombination rate. The minority carrier lifetime is the most critical parameter to determine the performance of MJ solar cells. Therefore, increasing the base minority carrier lifetime of the InGaN-based MJ solar cells increases efficiency.
The efficiency decreases with the increase in the surface recombination rate of the In1Ga1.N-based MJ solar cells. The efficiency of the solar cell is significantly lowered by increasing the surface recombination rate.
Fabrication Challenges in Monolithic MJ Solar cells
Band gap Matching
Since the band gaps of the materials used in a MJ solar cell determine which layer a photon is absorbed in, the band gaps determine how much energy can be obtained from each photon. Ideally, the difference between adjacent layers of the solar cell is approximately constant so that each layer can absorb an equal amount of the spectrum of incident light. Since the amount of excess energy from light converted to heat is equal to the difference between the photon energy and the band gap of the absorbing material, the difference between the band gaps should be made as small as possible.
The solar cell must also utilize as much of the spectrum as possible, so the top layer must have a high band gap and the bottom layer must have a small band gap. There is a design trade-off for a given number of layers of a Mi solar cell between having a small bandgap difference and bandgap covering a large one.
Lattice Matching
Lines between different materials represent semiconductors that are created by combining different amounts of the two materials. The vertical line going from InN to GaN represents the materials that are proposed to design MJ cells made of InGajN with different In compositions. Therefore, the monolithic stacking of the two materials results in a mesh-matched composite with different band gaps, minimizing thermal losses and maximizing efficiency.
Current Matching
Tunnel Junction
Figures 4.1-4.3 show the short-circuit current density Jsc, open-circuit voltage, V0, and conversion efficiency, 11, of InGaN-based MJ solar cells with and without considering the depletion width effect. Figures 4.17-4.19 show the effect of emitter thickness on Jsc, Voc and q of InGa1.N-based MJ solar cells. The open circuit voltage increases as the short circuit current of each junction increases using the concentrator.
Design of InGaN-based Mi Solar Cells
Introduction
The effect of temperature on the performance of the InGa1N-based multijunction solar cells under concentration is also evaluated.
Properties of InGa1 N
- Band gap, Eg
- Absorption Coefficient, a
InGaN-based Multijunction Solar Cells
- Cross-Sectional View
- Band Diagram
- Equivalent Circuit
All subcells are made of inGatN alloy with different compositions to achieve the required band gap. The subcells are arranged from bottom to top with lower to higher band gap. Tunnel joints are placed between the MJ layers to prevent joint formation and potential obstructions between the layers.
The band gap energies of the window layer and the back surface field layer (BSF) are higher than 4 that of the respective junction, which reflect electrons and electrons and reduce the carrier recombination.
Theoretical Design and Modeling
- Photocurrent Density
- Open Circuit Voltage
- Depletion Width
- Efficiency
For a sudden n-p junction solar cell with constant doping on each side of the junction, there are no electric fields crossing the depletion region in Fig. The short-circuit current density of the J50 tandem cell is given by the minimum photocurrent density produced. with tandem solar cell junctions. The saturated current density J0 was calculated for all InGaiN alloys using the following relationship [11]. where NA is the concentration of acceptor atoms per cm3 on the p side, ND is the concentration of donor atoms per cm3 on the n side, is not the concentration of the intrinsic carrier, j is the number of the Jth compound.
The open circuit voltage of an MJ cell is taken to be equal to the sum of the open circuit voltages of each junction. i =1, 2 ..n, n is the number of junction incorporated in the tandem cell. FF = 0.85 is considered throughout the thesis and 10 is the incident radiation per unit area in mW/cm2 whose value is taken from Ref.
Performance of InGaN-based Mi Solar Cells
Introduction
Performance of MJ Solar Cells
It has been found that the efficiency increases with the increase in the number of junctions due to the optimization of J5c and Voc. However, it is important to consider the effect of depletion width on efficiency to obtain accurate results.
Detailed Simulation Results of MJ Solar Cells
Effect of Band gap Optimization
However, after six junctions, the band gap energies are found to increase with the junction number.
Current Mismatch
Lattice Mismatch
Because the difference between the band gap of junction 5 and 6 of this solar cell is much compared to other junctions (table 4.3).
Conversion Efficiency of n-p MJ Solar Cells
- Effect of Surface Recombination Velocity
- Effect of Minority Carrier Life Time
- Effect of Emitter Thickness
- Effect of Doping Density
The figures show the dependence of Js, Voc and il on the base minority carrier lifetime (base diffusion length) of InGa1. The most significant effect of the minority base carrier lifetime is on the short circuit current density. Therefore, the efficiency increases by increasing the minority carrier lifetime of the In.Ga1 emitter.
The variation of efficiency with emitter-carrier concentration of 8-junction np cell is shown in Fig. The variation of efficiency with base carrier concentration of 8-junction np cell is shown in Fig.
Conversion Efficiency of p-n MJ Solar Cells
Finally, the efficiency is varied from 24.05% to 45.32% with increase in cross number from single to eight. The values of short-circuit current density, Jsc, open-circuit voltage, V0, and conversion efficiency, r, with the variation of the junction number for an n-p and p-n cell are also shown in Table 4.3.
Effect of Concentrator on Efficiency
- Introduction
- Concentrator Photovoltaic System
- Effect of Concentrator on Efficiency
- Effect of Temperature of mOaN-based MJ Solar Cells
Total global production of solar cells in the year 2001 was 400 MW, largely in the form of flat-plate Si solar cells. The temperature characteristics of the InGaN-based multijunction solar cells under concentration have not been evaluated in detail. The aim of this work is to study and design InGaiN-based multijunction solar cells for high performance.
Therefore, work can be done to account for the aforementioned effects on the design of InGaN-based MJ solar cells. Yamaguichi et al., "Japanese Research and Development Activities on Concentrator Solar Cells and ITT-V Modules", Proc.
Conclusions and Future Works
Conclusion
The efficiency increases rapidly for the first few junctions, and then the increasing tendency becomes slower with increasing number of junctions. The efficiency evaluated in this study was found to vary from 24.49 to 45.35% for solar cells with one to eight junctions. The band gap optimization effect increases the efficiency of the InGaiN-based MJ solar cell.
The increase in doping density increases the efficiency which is found about 51 % for eight junctions at carrier concentration 1x1020 cm 3. The efficiency with concentrator of each junction is found more than that of without concentrator.
Suggestion for Future Work
Kurtz, "Superior radiation resistance of IniGaN alloys: Full-solar-spectrum photovoltaic material system," Journal of Applied Physics, 94, pp. Karam, "Triple junction solar cell efficiencies above 32%: the promise and system challenges of their application in pv -high concentration ratio systems,” Proc. Henry, "Limiting efficiencies of ideal single and multiple energy gap terrestrial solar cells," Journal of Applied Physics, 5 1(8) pp.
Wurfel, "Improving Solar Cell Efficiency by Upconversion of Sub-Band-Gap Light," Journal of Applied Physics, 92, No. Alauddin "Study of Sodium Chlorate Production in a New Electrolytic Cell and Its Effect on Power Efficiency and Power Consumption." Journal of Applied Science and Technology, Vol.
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