Method for calculating carrier relaxation rate in wide bandgap top absorption layer in laminated solar cell

Abstract

The invention discloses a method for calculating the relaxation rate of a carrier in a wide bandgap top absorption layer in a laminated solar cell. An applicable object of the calculation method is a perovskite material with a wide forbidden band (greater than 1.7 eV), and main experimental data required by the method comprises a power-dependent steady-state photoluminescence spectrum of the applicable object; according to the calculation method, the hot carrier temperature under different excitation power densities is obtained through single exponential decay fitting, and the hot carrier temperature is substituted into a Pth (delta TC) equation to calculate the thermalization coefficient Qth of the excited state carrier, so that the relaxation rate of the excited state carrier is evaluated. The method can be used for accurately and quantitatively evaluating the carrier relaxation rate in the wide bandgap perovskite top layer material in the laminated solar cell.

Description

Technical Field

[0001] The invention relates to the technical field of characterization of high-efficiency thin-film photovoltaic materials, and in particular to a relaxation rate evaluation method based on excited-state carrier fitting temperature. Background Art

[0002] Both hot carrier solar cells and tandem solar cells improve their energy conversion efficiency by reducing or even avoiding the energy loss caused by hot carrier relaxation. The difference is that hot carrier solar cells try to extract the energy from the carriers before they cool down, that is, before their energy relaxes, thereby reducing the energy loss caused by the relaxation process, while tandem solar cells stack multiple solar cells with different band gaps together to reduce the energy loss caused by the mismatch between the semiconductor band gap and the energy of the incident photons. Applying the collection of hot carriers to tandem solar cells will further improve its ideal power conversion efficiency.

[0003] Therefore, effectively inhibiting or blocking the hot carrier relaxation process is crucial to realizing the concept of hot carrier batteries. The thermalization coefficient of carriers is a key parameter to measure the speed of the carrier relaxation process. However, the relaxation mechanism of the top absorber layer in the tandem solar cells is not clear, which leads to uncertainty in the selection of top absorber layer materials. Summary of the invention

[0004] Purpose of the invention: The purpose of the present invention is to accurately and quantitatively evaluate the carrier relaxation rate in wide bandgap perovskite top materials used in tandem solar cells, especially perovskite materials with wide bandgap (>1.7 eV).

[0005] Technical solution: The relaxation rate calculation method based on the excited state carrier fitting temperature of the present invention comprises the following steps:

[0006] 1. Select the A-site perovskite material of the wide bandgap top photovoltaic ternary and above of the tandem solar cell as the applicable object of this calculation method;

[0007] 2. Use the photoluminescence spectroscopy system to measure the energy-dependent steady-state photoluminescence spectra of the applicable object at different excitation power densities I SSPL (E);

[0008] 3. Energy-dependent steady-state photoluminescence spectra under different excitation power densities SSPL (E) Substitute it into the Maxwell-Boltzmann population formula and use the single exponential decay function to fit and calculate the carrier temperature T at different excitation power densities. C With ambient temperature T amb The temperature difference ΔT C =T C -T amb, in degrees Kelvin; the near Maxwell-Boltzmann population formula is:

[0009]

[0010] where k B The Boltzmann constant is 1.38×10 -23 J / K; ε(E) is the energy-dependent emissivity function; E is the wavelength energy in electron volts;

[0011] 4. The carrier temperature after self-excitation T C and the temperature difference ΔT from the ambient temperature C Substitute P th (ΔT C ) equation, the thermalization coefficient Q of the carrier is obtained by using the linear fitting function th , the P th (ΔT C ) equation is:

[0012]

[0013] Among them, P th is the thermalization rate of thermal energy. Since the rate at which the sample radiates energy is low, P th Approximately equal to the absorbed power density P abs , where P abs Equal to the product of the excitation power density and the absorption rate, E LO is the energy at the center of the Brillouin zone.

[0014] In step 3, a steady-state photoluminescence spectrum under an excitation power density is selected, and firstly, ln(I SSPL (E)) function graph, select the energy range corresponding to the linear part of the graph as the fitting range for carrier temperature calculation; within this range, the carrier temperature T is calculated using a single exponential decay function fitting. C With temperature difference ΔT C :

[0015]

[0016] Specifically, the baseline y0 of the single exponential decay function needs to be matched with ln(I SSPL (E)) is set on the same horizontal line, and t1=k is obtained according to the fitting results. B T C .

[0017] The step 4 specifically comprises: calculating the P obtained in step 3 th Substitute P th (ΔT C ) equation to obtain P th / exp(-E LO / (k B T C )), draw a graph about the temperature difference ΔT C P th / exp(-E LO / (k B T C ) linear relationship diagram, the slope value k in the linear relationship diagram is the thermalization coefficient Q th All carrier temperatures in the above calculations are in degrees Kelvin (K).

[0018] The ambient temperature of steps 3 and 4 is room temperature (295K).

[0019] Beneficial effects: Compared with the prior art, the advantages of the present invention are: First, the present invention can accurately and quantitatively calculate the thermalization coefficient Q of the top layer material of the wide bandgap perovskite used in the tandem solar cell th , thus evaluating its relaxation rate, especially in wide-bandgap perovskite semiconductor photovoltaic materials with a bandgap higher than 1.7eV, with good accuracy and reliability. Secondly, the calculated thermalization coefficient can make the selection of the top material of the tandem solar cell more convenient. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The material GA in the embodiment 0.03 [Cs 0.05 (FA 0.23 MA 0.77 ) 0.95 ] 0.97 PbIBr2 about the energy E ln (I SSPL (E)) Function graph;

[0021] Figure 2 The material GA in the embodiment 0.03 [Cs 0.05 (FA 0.23 MA 0.77 ) 0.95 ] 0.97 PbIBr2 on the absorption power density P abs The carrier temperature function diagram of ;

[0022] Figure 3 The material GA in the embodiment 0.03 [Cs 0.05 (FA 0.23 MA 0.77 ) 0.95 ] 0.97 PbIBr2 on temperature difference ΔT C P th / exp(-E LO / (kB T C ))Function graph. DETAILED DESCRIPTION

[0023] The present invention will be further explained below in conjunction with the embodiments and accompanying drawings:

[0024] 1. Select wide bandgap semiconductor materials as the applicable object of this calculation method. In this example, the applicable object is the perovskite film GA with a bandgap width of 2.0 eV. 0.03 [Cs 0.05 (FA 0.23 MA 0.77 ) 0.95 ] 0.97 PbIBr2 photovoltaic semiconductor materials;

[0025] 2. At room temperature of 295K, use the photoluminescence spectrum system to measure the energy-dependent steady-state photoluminescence spectrum of the applicable object I SSPL (E);

[0026] 3. Energy-dependent steady-state photoluminescence spectra under different excitation power densities SSPL (E) Substitute into the Maxwell-Boltzmann population formula to calculate the carrier temperature T at different excitation power densities C The temperature difference between the temperature and the ambient temperature ΔT C ; The near Maxwell-Boltzmann population formula is:

[0027]

[0028] The specific step is to select a steady-state photoluminescence spectrum under an excitation power density, first plot the ln(I SSPL (E)) Function graph, such as Figure 1 As shown in the figure, the energy range corresponding to the linear part of the figure is selected as the fitting range for carrier temperature calculation (i.e., 2.05-2.08 eV); within this range, the carrier temperature T is calculated by fitting using a single exponential decay function. C In the fitting, the baseline y0 of the single exponential decay function needs to be SSPL The bottom line of (E) is set on the same horizontal line, and the carrier temperature T is calculated based on t1 obtained from the fitting results. C , specifically T C =t1 / k B ; The single exponential decay function is:

[0029]

[0030] 4. The carrier temperature after self-excitation T C The temperature difference between the temperature and the ambient temperature ΔT C Substitute Pth (ΔT C ) equation, the thermalization coefficient Q of the carrier is calculated using the linear fitting function th , the equation is:

[0031]

[0032] Among them, P th is the thermalization rate of thermal energy. Since the rate at which the sample radiates energy is low, P th Approximately equal to the absorbed power density P abs , where P abs Equal to the product of the excitation power density and the absorption rate, E LO is the Brillouin zone center energy;

[0033] Specifically, the calculated carrier temperature difference ΔT under different excitation power densities is C and the thermalization rate P of thermal energy th Substitute P th (ΔT C ) equation to obtain ΔT C With P th / exp(-E LO / (k B T C )) is a linear function relationship, the slope value k of this function is the thermalization coefficient Q th (k=Q th ).

[0034] Figure 1 The GA is plotted under different absorption power density conditions. 0.03 [Cs 0.05 (FA 0.23 MA 0.77 ) 0.95 ] 0.97 Steady-state photoluminescence spectrum of PbIBr2. In this figure, the fitting area of ​​the high-energy tail region is represented by the shaded area, and the fitting process uses a single exponential decay function, combined with the near Maxwell-Boltzmann population formula, to calculate the carrier temperature.

[0035] Figure 2 The GA calculated from the fit is shown 0.03 [Cs 0.05 (FA 0.23 MA 0.77 ) 0.95 ] 0.97 The carrier temperature of PbIBr2 material at different absorption power densities. It can be observed from the figure that with the increase of absorption power density, the carrier temperature shows an upward trend.

[0036] Figure 3 For GA 0.03 [Cs 0.05 (FA 0.23 MA 0.77 ) 0.95 ] 0.97 Thermalization coefficient Q of PbIBr2 material th The fitted calculation diagram shows that the absorbed power density P abs And the exponential function exp(-E LO / k B T C ) ratio (unit: W·cm -2 ) is plotted as a function of the temperature difference ΔT (unit: K), and the fitted black dotted linear line shows a high degree of linearity, from which the thermalization coefficient Q can be determined th (Q th =k = 601.87 ± 6.48 mW·K -1 cm -2 ).

[0037] All carrier temperatures in the above calculations are in degrees Kelvin (K).

[0038] In this embodiment, the material GA is obtained by fitting calculation. 0.03 [Cs 0.05 (FA 0.23 MA 0.77 ) 0.95 ] 0.97 The thermalization coefficient of PbIBr2 and its error are Q th =601.87±6.48mW·K -1 cm -2 . Use this thermal coefficient to compare with the thermal coefficient of other materials Q th By comparison, the relaxation rate can be evaluated, thus providing a convenient reference for the selection of top-layer materials for tandem solar cells.

[0039] The present specification describes only the preferred embodiments of the present invention. However, for those skilled in the art, various modifications and adjustments can be made to the embodiments without departing from the basic principles and essence of the present invention. These modifications and adjustments should also be considered as part of the scope of protection of the present invention.

Claims

1. A method for calculating the carrier relaxation rate in the wide bandgap top absorption layer of a tandem solar cell, characterized in that: The following steps are involved: (1) Select the A-site perovskite material of the wide bandgap top photovoltaic ternary or above of the tandem solar cell as the applicable object of this calculation method; (2) Using the photoluminescence spectroscopy system to measure the energy-dependent steady-state photoluminescence spectra of the applicable object at different excitation power densities SSPL (E); (3) The energy-dependent steady-state photoluminescence spectra under different excitation power densities I SSPL (E) Substitute it into the Maxwell-Boltzmann population formula and use the single exponential decay function to fit and calculate the carrier temperature T at different excitation power densities. C With ambient temperature T amb The temperature difference ΔT C =T C -T amb , in degrees Kelvin; the near Maxwell-Boltzmann population formula is: where k B The Boltzmann constant is 1.38×10 -23 J / K; ε(E) is the energy-dependent emissivity function; E is the wavelength energy in electron volts; (4) The carrier temperature after self-excitation T C and the temperature difference ΔT from the ambient temperature C Substitute P th (ΔT C ) equation, the thermalization coefficient Q of the carrier is obtained by using the linear fitting function th , the P th (ΔT C ) equation is: Where P th is the thermalization rate of thermal energy. Since the rate at which the sample radiates energy is low, P th Approximately equal to the absorbed power density P abs , where P abs Equal to the product of the excitation power density and the absorption rate, E LO is the energy at the center of the Brillouin zone.

2. The method for calculating the carrier relaxation rate in the wide bandgap top absorption layer of a tandem solar cell according to claim 1, characterized in that: In the step (3), a steady-state photoluminescence spectrum I under an excitation power density is specifically selected. SSPL (E), plot the energy E with respect to ln(I SSPL (E)) function graph, select the energy range corresponding to the linear part of the graph as the fitting range for carrier temperature calculation; use the single exponential decay function y(x) to fit and calculate the carrier temperature T C , Its baseline y0 needs to be consistent with ln(I SSPL (E)) is consistent with the bottom line, and t1=k B T C ; The carrier and ambient temperature difference ΔT corresponding to the different excitation power densities calculated in step (4) C Substitute P th (ΔT C ) equation is changed to obtain about ΔT C With P th / exp(-E LO / (k B T C )) of the linear relationship diagram; the slope value k in the linear relationship diagram is the thermalization coefficient Q th , use this Q th Evaluate the relaxation rate of charge carriers.

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