Fine simulation method of CdTe-based II-VI group compound thin film solar cell

Abstract

The invention discloses a fine simulation method of a CdTe-based II-VI group compound thin film solar cell and a cell structure designed based on the method. According to the method, a physical model of a CdTe-based battery is established through numerical simulation, then the energy band structure of a carrier transport layer is systematically optimized, and the quantitative criteria that a hole transport layer needs to meet the requirements that the Fermi energy level is lower than that of an absorption layer and the hole transport layer has enough positive conduction band offset and an electron transport layer needs to have a wide band gap and moderate positive conduction band offset are determined. And for the optical layer, the optimal thickness of the antireflection layer is determined, the enhancement effect of the optical path gain of the textured structure on optical absorption is quantified, and the maximization of the light capture efficiency is realized. According to the method, through electrical-optical coupling simulation, the CdTe-based solar cell structure of which the conversion efficiency is remarkably improved can be accurately predicted and guided to be designed, the defects that a traditional experiment is high in trial and error cost and long in period are effectively overcome, and a reliable theoretical design and optimization tool is provided for research and development of a high-efficiency and low-cost CdTe-based solar cell.

Description

A refined simulation method for CdTe-based II-VI compound thin-film solar cells Technical Field

[0001] This invention belongs to the field of thin-film solar cell technology, specifically relating to a refined simulation design method for CdTe-based II-VI compound thin-film solar cells, which is particularly suitable for optimizing and predicting the structure and material parameters of high-efficiency, low-loss CdTe-based solar cells. Background Technology

[0002] Thin-film cadmium telluride (CdTe) solar cells have demonstrated significant competitiveness in the thin-film photovoltaic market due to their excellent stability, reliability, low manufacturing cost, and environmentally friendly characteristics, becoming a successful example of second-generation photovoltaic technology. Currently, First Solar in the United States has achieved an impressive conversion efficiency of 23.1%, but this still falls short of its theoretical limit of approximately 32%. See literature: Metzger, WK, Grover, S., Lu, D. et al., Nat Energy 4 (2019) 837-845; Burst, J., Duenow, J., Albin, D. et al., Nat Energy 1 (2016) 16015; Fiducia, TAM, Mendis, BG, Li, K. et al., Nat Energy 4 (2019) 504–511;Green, M., Dunlop, E., Yoshita, M., et al., Prog Photovolt Res Appl, 33(2025) 795-810; Sven Rühle., Solar Energy, 130 (2016) 139-147. Current key pathways for efficiency improvement include: replacing the traditional CdS window layer with wide-bandgap oxides (such as magnesium-doped zinc oxide MZO or SnO2) to reduce short-wavelength parasitic absorption; and introducing selenium to form narrow-bandgap CdSe. 1-x Te xInterface layering can extend the long-wavelength spectral response, passivate grain boundary defects, and prolong minority carrier lifetime. Furthermore, optimizing interface properties is also an important direction for suppressing carrier recombination and improving device performance. Interface recombination is not only affected by the defect density of states but also closely related to the energy level shift between the carrier transport layer and the absorption layer. See literature: Munshi, AH, Kephart, J., Abbas, A., et al., IEEEJ. Photovoltaics, 8 (2018) 310-314; Greenhalgh, R., Morris, K., Kornienko,V., et al., IEEE 49th Photovoltaics Specialists Conference, PVSC (2022) 900-903; Fiducia, TAM, Mendis, BG, Li, K., et al., Nat. Energy, 4 (2019)504-511; Fiducia, T., Howkins, A., Abbas, A., et al., Sol. Energy Mater. Sol. Cells, 238 (2022) 111595; Scarpulla, MA, McCandless, B., Phillips, AB, et al., Sol. Energy Mater. Sol. Cells 255 (2023) 112289; Kephart, JM, McCamy, JW, Ma, Z., et al., Sol. Energy Mater. Sol. Cell, 157 (2016), 266-275. Reducing carrier recombination at the CdTe-carrier transport layer interface is one of the key approaches to achieving efficiency breakthroughs of 25%. Existing studies have optimized front-end band alignment and reduced interfacial hole density by adjusting the Mg content in MZO; ZnTe:Cu, CuSCN, CuI, and other materials can be used as hole transport layers on the back surface to achieve ohmic contact and efficient hole transport. Therefore, a deeper understanding of band matching, defect formation, and carrier transport mechanisms in CdTe cells is of great significance.References: Song, T., Kanevce, A., Sites, JR, J. Appl. Phys, 119 (2016) 233104;Scarpulla, MA, McCandless, B., Phillips, et al., Sol. Energy Mater. Sol.Cells, 255 (2023) 112289; Kuciauskas, D., Farrell, S., Dippo, P., J. Appl. Phys. 116 (2014) 123108; Duenow, JN, Metzger, WK, J. Appl. Phys. 125(2019) 053101; Wu, X., Zhou, J., Duda, A., Thin Solid Films, 515 (2007) 5798-5803. Traditional experimental optimization methods are costly and time-consuming, while numerical simulation can provide efficient and economical theoretical guidance for device structure design and performance prediction. Therefore, this invention proposes a refined simulation method for CdTe-based II-VI group thin-film solar cells. By systematically optimizing the carrier transport layer band structure and optical management characteristics, it provides a reliable design basis for realizing high-efficiency CdTe solar cells. Summary of the Invention

[0003] This invention aims to provide a refined simulation method for CdTe-based II-VI compound thin-film solar cells. By establishing a systematic numerical simulation framework, the method accurately optimizes the carrier transport layer band structure and optical management characteristics of CdTe cells, thereby theoretically overcoming the limitations of traditional trial-and-error experiments and efficiently guiding the design and fabrication of high-efficiency, low-cost CdTe solar cells. The technical solution of this invention is as follows: A refined simulation method for CdTe-based II-VI compound thin-film solar cells includes the following steps: 1. Device physical modeling: Based on the fundamental semiconductor equations (Poisson equation, continuity equation, carrier transport equation), a numerical simulation model of the CdTe solar cell is established under standard test conditions (AM1.5G spectrum, 100 mW / cm² light intensity, 300 K temperature). The initial structure includes a transparent conductive layer (such as ITO), an electron transport layer (such as CdS), a CdTe absorption layer, and a hole transport layer (such as ZnTe:Cu). 2. Carrier Transport Layer Bandwidth Optimization: 2.1 Hole Transport Layer Screening and Design: By simulating and comparing various hole transport materials (such as ZnTe:Cu, CuO, MoSe2, Sb2S3, NiO), the effects of their bandwidth alignment with CdTe, Fermi level shift, and interface electric field on device performance are analyzed. The optimal hole transport layer must satisfy the following conditions: its Fermi level is lower than that of CdTe to form a positive interface electric field, and its conduction band shift is a suitable positive value to effectively reflect electrons. 2.2 Electron Transport Layer Screening and Design: By simulating and comparing various electron transport materials (such as CdS, MZO, ZnS, ZnSe, Nb2O5), their bandgap, conduction band shift, and their effects on parasitic absorption and interface recombination are analyzed. The optimal electron transport layer must satisfy the following conditions: a wide bandgap (>3.3 eV) to reduce short-wavelength light loss, and a moderate positive conduction band shift (0.1–0.3 eV) with CdTe to promote electron extraction and suppress recombination. 3. Optical Management Optimization: Based on the optimized electrical structure, MgF2 is introduced as an antireflection layer, and the thickness of the antireflection layer is optimized. A textured structure is introduced into the CdTe absorption layer for optical simulation. The enhancement effect of the textured structure on light absorption is quantified by calculating the optical path length, maximizing the light capture efficiency across the entire spectrum. 4. Performance Prediction and Structural Output: Combining the above electrical and optical optimization results, the current-voltage characteristics, external quantum efficiency, and photoelectric conversion efficiency of the final device are predicted, and a complete optimized battery structure scheme is output. The features of this invention are: 1. Systematic Optimization Path: The carrier transport layer bandgap engineering and optical management are coupled and simulated to achieve synergistic optimization of electrical and optical performance. 2. Quantitative Design Criteria: Quantitative screening criteria for efficient hole transport layers (Fermi level below CdTe and with sufficient positive conduction band offset) and electron transport layers (wide bandgap and with moderate positive conduction band offset) are clearly defined.3. Optical Loss Optimization: An antireflection layer was added and its thickness optimized (80nm MgF2) to simulate the enhancement effect of Yablonovitch-limited optical path gain on light absorption. 4. Efficient Experimental Guidance: Simulation significantly reduces experimental trial-and-error costs and timelines, providing a clear and reliable theoretical design blueprint for the development of high-efficiency CdTe solar cells. Figure 1 is a schematic diagram of a CdTe-based II-VI compound thin-film solar cell structure. Figure 2 shows the output characteristics of a cell with different hole transport layers. Figure 3 shows the effect of Fermi level shift and conduction band shift of the hole transport layer on cell efficiency. Figure 4 shows the output characteristics of a cell with different electron transport layers. Figure 5 shows the effect of bandgap and conduction band shift of the electron transport layer on cell efficiency. Figure 6 shows the optical loss analysis of the cell before and after optical management optimization. Figure 7 shows the output characteristics of the cell before and after optimization. Figure 8 is a schematic diagram of a performance optimization technology roadmap for CdTe-based II-VI compound thin-film solar cells. Detailed Implementation Example: A refined simulation method for CdTe-based II-VI compound thin-film solar cells includes the following steps: 1. Establishing a basic simulation model: Using wxAMPS 3 software, an initial cell structure model is established: ITO (70 nm) / CdS (50 nm) / CdTe (2000 nm) / ZnTe:Cu (50 nm), as shown in Figure 1. The simulation conditions are set as AM1.5G spectrum, 100 mW / cm², and 300K. 2. Optimizing the hole transport layer: 2.1 The hole transport layer material is successively replaced with CuO, MoSe2, Sb2S3, and NiO for simulation comparison, as shown in Figure 2. 2.2 The analysis results show that NiO, due to its suitable Fermi level position (lower than CdTe) and conduction band shift, can form a favorable interfacial electric field and suppress electron recombination, thus significantly improving the device efficiency. Further parameter scanning determined that the optimal initial Fermi level shift (IFLO) should be ≥0.1 eV and the conduction band shift (CBO) should be ≥0.4 eV, as shown in Figure 3. 3. Optimization of the electron transport layer: 3.1 Simulations were performed by sequentially replacing the electron transport layer material with MZO, ZnS, ZnSe, and Nb2O5, as shown in Figure 4. 3.2 Analysis results show that the wide bandgap Nb2O5 can effectively reduce short-wavelength parasitic absorption and increase short-circuit current. Further parameter scanning determined that its optimal bandgap should be >3.3 eV, and the conduction band shift (CBO) compared with CdTe should be between 0.1–0.3 eV, as shown in Figure 5. 4. Optimization of the optical structure: 4.1 Based on the optimized structure ITO / Nb2O5 / CdTe / NiO, MgF2 of different thicknesses was set as an antireflection layer, and textured optical simulations were performed on the CdTe layer. 4.2 Analysis results show that the optimal thickness of MgF2 is 80 nm, which can effectively reduce optical losses caused by reflection. The optical path gain of the textured structure should reach the Yablonovitch limit, and the light absorption enhancement effect of this structure is quantitatively calculated. Increasing the optical path significantly enhances long-wavelength light absorption, as shown in Figure 6. 5. Output the final optimization results: 5.1 After the above three optimization steps, the simulated predicted photoelectric conversion efficiency of the battery increased from the initial 20.95% to 25.07%, as shown in Figure 7. 5.2 Output the complete optimized battery structure parameters, JV curve, EQE spectrum, and efficiency improvement path diagram, as shown in Figure 8, providing specific guidance for experimental fabrication. Application effects: This simulation method systematically reveals the key interface band factors and optical mechanisms affecting the performance of CdTe batteries, providing clear material selection and structural design guidelines. Battery design guided by this method is expected to achieve significant efficiency improvements in experiments and effectively reduce R&D costs and time.The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A refined simulation method for CdTe-based II-VI compound thin-film solar cells, characterized in that, Includes the following steps: (1) Establishing a basic simulation model: Based on the basic equations of semiconductors, an initial battery numerical simulation model including a transparent conductive layer, an electron transport layer, a CdTe-based II-VI compound thin film absorption layer and a hole transport layer is established under standard test conditions; (2) Optimization of the carrier transport layer band structure: By simulating and comparing the electron transport layer and hole transport layer of different materials, the band matching, Fermi level shift and interface electric field distribution of the absorption layer are analyzed to determine the optimal carrier transport layer material and its band structure parameters; (3) Optimization of optical management: Based on the optimized electrical structure, an anti-reflection layer is added and its thickness is optimized. The absorption layer is subjected to textured optical simulation. The enhancement of light absorption is quantified by calculating the optical path to maximize the light capture efficiency; (4) Performance prediction and structure output: Based on the combined electrical and optical optimization results, predict the performance indicators of the final device and output a complete optimized battery structure scheme.

2. The refined simulation method according to claim 1, characterized in that, The optimization criterion for the hole transport layer in step (2) is: the Fermi level of the selected hole transport layer should be lower than that of the absorption layer in order to form a positive interface electric field that is conducive to hole extraction. Its conduction band offset from the absorption layer should be positive, and its absolute value should not be less than 0.4 eV, so as to effectively reflect electrons and suppress interface recombination.

3. The refined simulation method according to claim 1, characterized in that, The optimization criteria for the electron transport layer in step (2) are as follows: the selected electron transport layer should be a wide bandgap material with a bandgap width greater than 3.3 eV to reduce short-wave parasitic absorption; its conduction band offset from the absorption layer should be a positive value between 0.1 eV and 0.3 eV to promote electron extraction and effectively suppress interface recombination.

4. The refined simulation method according to claim 1, characterized in that, The optical management optimization mentioned in step (3) refers to: the optimal thickness of the MgF2 antireflection layer is 80nm to reduce reflection loss caused by interference; the optical path gain of the textured structure should reach the Yablonovitch limit to maximize the optical path gain and enhance long-wavelength light capture.

5. The refined simulation method according to claim 1, characterized in that, The standard test conditions are AM1.5G solar spectrum, 100 mW / cm² light intensity, and 300 K temperature.

6. The refined simulation method according to claim 1, characterized in that, The fundamental equations of semiconductors include the Poisson equation, the continuity equation for electrons and holes, and the carrier transport equation.

7. A CdTe-based thin-film solar cell designed by the fine simulation method described in any one of claims 1-6, characterized in that, Its structure includes, in sequence: a transparent conductive layer, an electron transport layer, a CdTe-based II-VI compound thin film absorption layer, a hole transport layer, and a metal back electrode; wherein, the materials and band structure parameters of the electron transport layer and the hole transport layer, as well as the surface texture of the antireflection layer and the absorption layer, are all optimized and determined by the fine simulation method.

8. The CdTe-based thin-film solar cell according to claim 7, characterized in that, The CdTe-based II-VI compound thin film absorber layer material is selected from at least one of CdTe, CdSeTe, CdMgTe, CdZnTe, or other CdTe-based alloy materials; the electron transport layer material is selected from at least one of CdS, CdS:O, CdSe, ZnS, ZnSe, SnO2, ZnO, MZO, and Nb2O5; the hole transport layer material is selected from CuO, Cu x Te, MoSe2, Sb2S3, NiO, CuSCN, CuI, MoO x At least one of V2O5 or ZnTe:Cu.

9. The CdTe-based thin-film solar cell according to claim 7, characterized in that, The transparent conductive layer is an In2O3-based, SnO2-based, or ZnO-based transparent conductive thin film material, and the metal back electrode contains at least one of Au, Ag, Al, or Cu.

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