A method for bandgap combination optimization of multi-junction solar cells

Abstract

This invention discloses a method for optimizing the bandgap combination of multi-junction solar cells. By setting the calculation step size and the number of calculation steps for each junction's bandgap, the method subdivides the bandgap interval, accurately calculates the photoelectric conversion efficiency of multi-junction solar cells under different bandgap combinations, and compares the maximum photoelectric conversion efficiency under various bandgap combinations to obtain the optimal bandgap combination. This invention enables rapid calculation of the optimal bandgap combination for multi-junction solar cells, thereby improving the efficiency of solar cells.

Description

Technical Field

[0001] This invention belongs to the field of solar cells, specifically relating to a method for optimizing the bandgap combination of multi-junction solar cells. Background Technology

[0002] In recent years, photovoltaic power generation has developed rapidly as an important renewable energy technology. Currently, any single-junction solar cell has an efficiency limit: the Shockley-Queisser limit (SQ). The maximum efficiency calculated for the SQ limit of modern single-junction solar cells is around 33%. This is because the photoelectric response spectrum of any single semiconductor material can only effectively convert a certain range of light energy in the solar spectrum into electrical energy, fundamentally limiting the improvement of efficiency. Combining semiconductor materials with different band gaps to form multi-junction solar cells, which absorb and convert sunlight of different wavelength ranges respectively, can effectively improve the efficiency of solar cells. For example, the mainstream structure of traditional gallium arsenide multi-junction cells is a GaInP / GaInAs / Ge triple-junction solar cell composed of GaInP, GaInAs, and Ge sub-cells. The overall cell structure maintains lattice matching, with a band gap combination of 1.85 / 1.40 / 0.67 eV. However, this multi-junction cell structure is not optimal for the solar spectrum. This is because there is a significant bandgap difference between GaInAs and Ge sub-cells. The short-circuit current of the Ge bottom cell can be nearly twice that of the middle and top cells. Due to the current limitation of the series structure, a large portion of solar energy cannot be fully converted and utilized, thus limiting the improvement of cell performance. Furthermore, with the development of four-junction, six-junction, and even more-junction solar cells, the number of junctions in multi-junction solar cells is increasing, making the bandgap combination arrangement of multi-junction solar cells increasingly complex. Existing experimental research cannot obtain the optimal bandgap combination for multi-junction solar cells. Summary of the Invention

[0003] The purpose of this invention is to provide a method for optimizing the bandgap combination of multi-junction solar cells, which can quickly calculate the optimal bandgap combination of multi-junction solar cells and improve the efficiency of solar cells.

[0004] The technical solution adopted in this invention is:

[0005] A method for optimizing the bandgap combination of multi-junction solar cells is proposed. By setting the calculation step size and the number of calculation steps for each junction's bandgap, the bandgap interval is subdivided, and the photoelectric conversion efficiency of multi-junction solar cells under different bandgap combinations is accurately calculated. The maximum photoelectric conversion efficiency under various bandgap combinations is compared to obtain the optimal bandgap combination.

[0006] The method includes the following steps:

[0007] S1: Let the number of junctions in a multi-junction solar cell be n, and let the junctions from the top junction at the top of the cell to the bottom junction at the bottom be J1, J2, ..., Jn, where J1 is the top junction and Jn is the bottom junction.

[0008] An incident light with power Pi strikes the surface of a solar cell perpendicularly, passing through the top junction J1 and reaching the bottom junction Jn in sequence; let the band gap of each junction J1, J2, ..., Jn be variables G1, G2, ..., Gn respectively.

[0009] S2: Let the initial values ​​of the band gap of the n junctions of a multi-junction solar cell be G1_1, G2_1, ..., Gn_1; let the calculation step size of the band gap of each junction be t, and the calculation step number of each junction be m, then the band gap value calculated in the y-th step of the x-th junction is Gx_y=Gx_1+t×(y-1), where 1≤x≤n, 1≤y≤m;

[0010] S3: Generate an orthogonal parameter table L based on the values ​​of x and y, and store L as a two-dimensional array; determine the parameter combination based on the formula for calculating orthogonal parameters of equal level, and obtain the maximum number of calculations q;

[0011] S4: Calculate the photocurrent arrays I1, I2, ..., In for each junction J1, J2, ..., Jn of a multi-junction solar cell, and the corresponding photovoltage arrays V1, V2, ..., Vn.

[0012] Let the optimal photocurrent of each junction in the z-th calculation be I1_z, I2_z, ..., In_z, where 1≤z≤q; compare the photocurrents I1_z, I2_z, ..., In_z of the n junctions and find the minimum value; assign the value of the minimum value to the variable Iz_min;

[0013] Read the array of photogenerated voltages corresponding to the photogenerated current of each junction J1, J2, ..., Jn when it is Iz_min, and assign the values ​​to V1_z, V2_z, ..., Vn_z respectively. Calculate the sum ∑z of the photogenerated voltages V1_z, V2_z, ..., Vn_z, and assign the value to the variable Vz_sum. Calculate the efficiency Pz of the multi-junction solar cell in the z-th iteration, Pz = (Iz_min * Vz_sum) / Pi;

[0014] S5: After completing q calculations, compare the values ​​of P1, P2, ..., Pq, find the maximum value, and assign the maximum value to the variable Pmax; assign the bandgap value combination G1, G2, ..., Gn corresponding to the maximum value Pmax to the one-dimensional array G_opt; then the one-dimensional array G_opt is the optimal bandgap combination of the n-junction solar cell.

[0015] According to the above scheme, the number of junctions n of the multi-junction solar cell is not less than 3 junctions.

[0016] According to the above scheme, in S1, the spectral power wavelength distribution of the incident light is the standard solar light source AM0, the standard solar light source AM1.5, or a custom function distribution, such as the blackbody radiation spectral distribution, the monochromatic laser spectral distribution, etc.

[0017] According to the above scheme, in S2, the range of the calculation step size t for the bandgap of each junction is: 0.01eV≤t≤0.1eV.

[0018] According to the above scheme, in S4, the optimal photocurrent Ix_z of the x-th junction is the current value at the point where the photovoltaic power output of the junction is at its maximum.

[0019] According to the above scheme, in S4, the photocurrent arrays I1, I2, ..., In of each junction J1, J2, ..., Jn of the multi-junction solar cell, and the photovoltage arrays V1, V2, ..., Vn corresponding to the photocurrents are calculated based on the detailed balance theory method.

[0020] The beneficial effects of this invention are:

[0021] This invention can quickly calculate the theoretical efficiency of bandgap combinations of multiple junctions, obtain the optimal bandgap combination of n-junction solar cells, and thus guide the design of solar cell device structures, saving manpower, material resources and time costs.

[0022] This invention takes into account the current limitation of series battery circuits, and can quickly optimize the bandgap of other junction cells under the condition of limiting part of the bandgap, thereby obtaining the theoretically optimal multi-junction cell bandgap combination, thus providing guidance for experiments;

[0023] This invention solves the current matching problem, making the selection of bandgap and quantum well number of different sub-cells more flexible in the design, while meeting the bandgap requirements of the front cell and the back cell respectively, laying the foundation for the development of multi-junction solar cells. Attached Figure Description

[0024] The present invention will be further described below with reference to the accompanying drawings and embodiments. In the accompanying drawings:

[0025] Figure 1 This is a flowchart illustrating the method for optimizing the bandgap combination of multi-junction solar cells.

[0026] Figure 2 This is the IV curve of a 3-junction solar cell after optimization of the bandgap combination;

[0027] Figure 3 This is the IV curve of a 6-junction solar cell after optimization of the bandgap combination. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0029] Example 1

[0030] This embodiment provides a method for optimizing the bandgap of a three-junction solar cell, including:

[0031] S1: The number of junctions in the multi-junction solar cell is set to 3, with the top junction at the top of the cell and the bottom junction at the bottom designated as J1, J2, and J3, respectively, where J1 is the top junction and J3 is the bottom junction; the incident light is assumed to be space sunlight (AM0 spectrum), and the incident light power is Pi = 1350 W / m. 2 And it is vertically irradiated onto the surface of the solar cell, passing through the top junction J1 and reaching the bottom junction J3 in sequence; the band gap of each junction of J1, J2, and J3 is set to variables G1, G2, and G3 in sequence.

[0032] S2: Let the initial values ​​of the band gaps of the three junctions of a multi-junction solar cell be G1_1, G2_1, and G3_1, respectively; let the calculation step size of the band gap of each junction be 0.01 eV, and let the calculation number of each junction be 20; then the band gap value calculated in the y-th step of the x-th junction is Gx_y = Gx_1 + 0.01 × (y-1), where 1 ≤ x ≤ 3, 1 ≤ y ≤ 20;

[0033] S3: Generate an orthogonal parameter table L based on the values ​​of x and y, and store L as a two-dimensional array; determine the parameter combination according to the formula for calculating orthogonal parameters of equal level, and the number of combination calculations is n = 3 × (2 × (20-1) + 1) = 117; the maximum number of calculations is 117.

[0034] S4. Based on the detailed balance theory method, calculate the photocurrent arrays I1, I2, I3 of each junction J1, J2, J3 of the multi-junction solar cell, as well as the photovoltage arrays V1, V2, V3 corresponding to the photocurrents.

[0035] Let the optimal photocurrents of each junction in the z-th calculation be I1_z, I2_z, and I3_z, where 1 ≤ z ≤ 117; compare the photocurrents I1_z, I2_z, and I3_z of the three junctions, find the minimum value, and assign the value of the minimum value to the variable Iz_min; read the array of photovoltages corresponding to the photocurrents of each junction J1, J2, and J3 when the photocurrent is Iz_min, and assign the values ​​to V1_z, V2_z, and V3_z respectively; calculate the sum of the photovoltages V1_z, V2_z, and V3_z, ∑z, and assign the value to the variable Vz_sum; then the efficiency of the multi-junction solar cell calculated in the z-th time is Pz = (Iz_min * Vz_sum) / Pi;

[0036] S5: After completing 117 calculations, compare the values ​​of P1, P2...P117, find the maximum value, assign the maximum value to the variable Pmax, and assign the bandgap value combination G1, G2...G6 corresponding to the maximum value Pmax to the one-dimensional array G_opt; then the one-dimensional array G_opt is the optimal bandgap combination of the three-junction solar cell. Figure 2 The figure shows the IV curves corresponding to the optimal bandgap combination of a 3-junction solar cell. The bandgap values ​​for the corresponding 3-junction combinations are: G1 = 1.84 eV, G2 = 1.21 eV, and G3 = 0.77 eV.

[0037] Example 2

[0038] This embodiment provides a method for optimizing the bandgap of a six-junction solar cell, including:

[0039] S1: The number of junctions in the multi-junction solar cell is set to 6, with the top junction at the top of the cell and the bottom junction at the bottom numbered J1, J2, J3, J4, J5, and J6, respectively. J1 is the top junction, and J6 is the bottom junction. The incident light is terrestrial sunlight (AM1.5 spectrum), and the incident light power is Pi = 1000 W / m. 2 And it is vertically irradiated onto the surface of the solar cell, passing through the top junction J1 and reaching the bottom junction J6 in sequence; the band gap of each junction of J1, J2, J3, J4, J5, and J6 is set to variables G1, G2, G3, G4, G5, and G6 in sequence.

[0040] S2: Let the initial values ​​of the band gaps G1, G2, G3, G4, G5, and G6 of the six junctions of a multi-junction solar cell be G1_1, G2_1, ..., G6_1, respectively; let the calculation step size of the band gap for each junction be 0.01 eV, and the number of calculation steps for each junction be 30; then the band gap value calculated for the x-th junction at the y-th step is Gx_y = Gx_1 + 0.01 × (y-1), where 1 ≤ x ≤ 6, 1 ≤ y ≤ 30;

[0041] S3: Generate an orthogonal parameter table L based on the values ​​of x and y, and store L as a two-dimensional array; determine the parameter combination according to the formula for calculating orthogonal parameters of equal level, and the number of combination calculations is n = 15 × (2 × (30-1) + 1) = 885, so the maximum number of calculations is 885;

[0042] S4: Calculate the photocurrent arrays I1, I2, ..., I6 for each junction J1, J2, J3, J4, J5, J6 of a multi-junction solar cell, and the corresponding photovoltage arrays V1, V2, ..., V6.

[0043] Let the optimal photocurrent of each junction in the z-th calculation be I1_z, I2_z, ..., In_z, where 1≤z≤885; compare the photocurrents I1_z, I2_z, ..., In_z of the six junctions, find the minimum value, and assign the value of the minimum value to the variable Iz_min;

[0044] Read the array of photogenerated voltages corresponding to the photogenerated current of each junction J1, J2, J3, J4, J5, and J6 when it is Iz_min, and assign the values ​​to V1_z, V2_z, ..., V6_z respectively; calculate the sum ∑z of the photogenerated voltages V1_z, V2_z, ..., V6_z, and assign the value to the variable Vz_sum; calculate the efficiency of the multi-junction solar cell in the z-th iteration as Pz = (Iz_min * Vz_sum) / Pi;

[0045] S5: After completing 885 calculations, compare the values ​​of P1, P2, ..., P885, find the maximum value, and assign the maximum value to the variable Pmax. Assign the bandgap value combination G1, G2, ..., G6 corresponding to the maximum value Pmax to the one-dimensional array G_opt. Then, the one-dimensional array G_opt is the optimal bandgap combination of the 6-junction solar cell. Figure 3 The figure shows the IV curves corresponding to the optimal bandgap combination of a 6-junction solar cell. The bandgap values ​​for the corresponding 6-junction combinations are: G1 = 2.25 eV, G2 = 1.75 eV, G3 = 1.35 eV, G4 = 1.08 eV, G5 = 0.82 eV, and G6 = 0.58 eV.

[0046] It should be understood that those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A method for optimizing the bandgap combination of multi-junction solar cells, characterized in that: By setting the calculation step size and the number of calculation steps for each junction's bandgap, the bandgap range is subdivided, and the photoelectric conversion efficiency of multi-junction solar cells under different bandgap combinations is accurately calculated. The maximum photoelectric conversion efficiency under various bandgap combinations is compared to obtain the optimal bandgap combination. The method specifically includes the following steps: S1: Let the number of junctions in a multi-junction solar cell be n, and let the junctions from the top junction at the top of the cell to the bottom junction at the bottom be J1, J2, ..., Jn, where J1 is the top junction and Jn is the bottom junction. An incident light with power Pi strikes the surface of a solar cell perpendicularly, passing through the top junction J1 and reaching the bottom junction Jn in sequence; let the band gap of each junction J1, J2, ..., Jn be variables G1, G2, ..., Gn respectively. S2: Let the initial values ​​of the band gap of the n junctions of a multi-junction solar cell be G1_1, G2_1, ..., Gn_1; let the calculation step size of the band gap of each junction be t, and the number of calculation steps of each junction be m, then the band gap value calculated in the y-th step of the x-th junction is Gx_y = Gx_1 + t × (y-1), where 1 ≤ x ≤ n, 1 ≤ y ≤ m; S3: Generate an orthogonal parameter table L based on the values ​​of x and y, and store L as a two-dimensional array; determine the parameter combination based on the formula for calculating orthogonal parameters of equal level, and obtain the maximum number of calculations q; S4: Calculate the photocurrent arrays I1, I2, ..., In for each junction J1, J2, ..., Jn of a multi-junction solar cell, and the corresponding photovoltage arrays V1, V2, ..., Vn. Let the optimal photocurrent of each junction in the z-th calculation be I1_z, I2_z, ..., In_z, where 1≤z≤q; compare the photocurrents I1_z, I2_z, ..., In_z of the n junctions and find the minimum value; assign the value of the minimum value to the variable Iz_min; Read the array of photogenerated voltages corresponding to the photogenerated current of each junction J1, J2, ..., Jn when it is Iz_min, and assign the values ​​to V1_z, V2_z, ..., Vn_z respectively. Calculate the sum ∑z of the photogenerated voltages V1_z, V2_z, ..., Vn_z, and assign the value to the variable Vz_sum. Calculate the efficiency Pz of the multi-junction solar cell in the z-th iteration, Pz = (Iz_min * Vz_sum) / Pi; S5: After completing q calculations, compare the values ​​of P1, P2, ..., Pq, find the maximum value, and assign the maximum value to the variable Pmax; assign the bandgap value combination G1, G2, ..., Gn corresponding to the maximum value Pmax to the one-dimensional array G_opt; then the one-dimensional array G_opt is the optimal bandgap combination of the n-junction solar cell.

2. The method for optimizing the bandgap combination of multi-junction solar cells according to claim 1, characterized in that: In S4, the photocurrent arrays I1, I2, ..., In and the photovoltage arrays V1, V2, ..., Vn corresponding to each junction J1, J2, ..., Jn of the multi-junction solar cell are calculated based on the detailed balance theory method.

3. The method for optimizing the bandgap combination of multi-junction solar cells according to claim 1, characterized in that: The number of junctions n in the multi-junction solar cell is not less than 3.

4. The method for optimizing the bandgap combination of multi-junction solar cells according to claim 1, characterized in that: In S1, the spectral power wavelength distribution of the incident light is either standard solar light source AM0 or standard solar light source AM1.

5.

5. The method for optimizing the bandgap combination of multi-junction solar cells according to claim 1, characterized in that: In S2, the calculation step size t for the bandgap of each junction is in the range of 0.01eV≤t≤0.1eV.

6. The method for optimizing the bandgap combination of multi-junction solar cells according to claim 1, characterized in that: In S4, the optimal photocurrent Ix_z of the x-th junction is the current value at the point where the photovoltaic power output of that junction is at its maximum.

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