CN-115985802-B - Test method for surface recombination of crystalline silicon

CN115985802BCN 115985802 BCN115985802 BCN 115985802BCN-115985802-B

Abstract

The invention relates to the technical field of solar cells and discloses a test method for surface recombination of crystalline silicon, which comprises the steps of preparing a silicon wafer sample comprising a calibration area and a test area, testing to obtain an excess carrier concentration value delta n of the calibration area under different light intensities, testing to obtain a spatially resolved photoluminescence PL brightness value of the whole silicon wafer sample under different light intensities, obtaining a calibration constant C according to the average delta n and the average PL brightness value of the calibration area, obtaining a spatially resolved delta n of the whole silicon wafer sample under different light intensities according to the C and the spatially resolved PL brightness value, obtaining a spatially resolved minority carrier lifetime tau eff of the whole silicon wafer sample under different light intensities according to the C and the spatially resolved delta n, and obtaining a spatially resolved surface recombination value J 0 of the whole silicon wafer sample under different injection concentrations according to the spatially resolved tau eff and the spatially resolved delta n. The method has high spatial resolution and accuracy, can accurately obtain the independent surface composite values under different injection concentrations, and has short time consumption.

Inventors

BAO JIE
HUANG CE
ZHANG GENG
JI GENHUA
Shen Chenghuan
Du Zheren

Assignees

泰州中来光电科技有限公司

Dates

Publication Date: 20260508
Application Date: 20230213
Priority Date: 20220930

Claims (9)

1. The test method of the crystalline silicon surface recombination is characterized by comprising the following test steps: The method comprises the steps of S1, preparing a silicon wafer sample by adopting a monocrystalline silicon substrate, wherein the silicon wafer sample comprises a calibration area and a test area, the calibration area is a square area with the size not less than 4cm and 4cm, the test area is a square area with the side length of micron-sized, the passivation performance of the test area is different from that of the calibration area, and the passivation performance of each position in the calibration area is uniform, so that the difference of surface composite values of each position in the calibration area is not more than 10%; s2, testing the calibration area to obtain an excess carrier concentration value delta n of the calibration area under different light intensities; S3, testing the whole silicon wafer sample to obtain a spatially resolved photoluminescence PL brightness value of the whole silicon wafer sample under different light intensities; Step S4, obtaining a calibration constant C according to the average excess carrier concentration value delta n and the average spatially resolved photoluminescence PL brightness value of the calibration area; S5, according to the calibration constant C and the spatially resolved photoluminescence PL brightness value, obtaining a spatially resolved excess carrier concentration value delta n of the whole silicon wafer sample under different light intensities; Step S6, according to the calibration constant C and the spatial resolution excess carrier concentration value delta n, obtaining the spatial resolution minority carrier lifetime tau eff of the whole silicon wafer sample under different light intensities; Step S7, obtaining a spatial resolution surface composite value J 0 of a whole silicon wafer sample under different injection concentrations according to the spatial resolution minority carrier lifetime tau eff and the spatial resolution excess carrier concentration value delta n; in the step S7, according to the spatially resolved minority carrier lifetime τ eff and the spatially resolved excess carrier concentration value Δn, a spatially resolved surface recombination value J 0 of the whole silicon wafer sample under different injection concentrations is obtained by the following formula: Wherein J 0 is the spatial resolution surface recombination value of the silicon wafer sample under different injection concentrations, delta n is the spatial resolution excess carrier concentration value of the silicon wafer sample under different light intensities, q is the unit charge quantity of the silicon wafer sample, the size is 1.6X10 -19 C, W is the thickness of the monocrystalline silicon substrate, n i is the intrinsic carrier concentration of the silicon wafer sample, and the size is 8.6X10 9 cm -3 ; Wherein, the Where τ cor is the corrected minority carrier lifetime, τ eff is the minority carrier lifetime of the silicon wafer sample, τ Auger is the auger recombination lifetime of the silicon wafer sample, τ bulk,SRH is the bulk region SRH recombination lifetime of the silicon wafer sample, 1/τ bulk,SRH is a constant when the implantation concentration is constant, and N doped is the doping concentration of the single crystal silicon substrate.
2. The method according to claim 1, wherein in the step S1, the single crystal silicon substrate has an N-type or P-type conductivity; the test area is a square area with the side length not less than 1 mu m; The difference in passivation properties between the test and calibration regions includes a difference in doping, structure, and/or passivation anti-reflective film between the test and calibration regions.
3. The method for testing surface recombination of crystalline silicon according to claim 1 or 2, wherein the silicon wafer sample comprises a single crystal silicon substrate, and passivation antireflection films are provided on front and rear surfaces of the single crystal silicon substrate.
4. The method according to claim 1, wherein in the step S2, the WCT-120 minority carrier lifetime tester is used to measure the excess carrier concentration value Δn of the calibration area under different light intensities.
5. The method for testing surface recombination of crystalline silicon according to claim 1, wherein the step S3 specifically comprises the following steps: s31, measuring a spatially resolved photoluminescence PL brightness map of a whole silicon wafer sample under different light intensities by using PL equipment; And S32, obtaining the spatially resolved photoluminescence PL brightness values of the whole silicon wafer sample under different light intensities according to the spatially resolved photoluminescence PL brightness map.
6. The method for testing surface recombination of crystalline silicon according to claim 1, wherein the step S4 specifically comprises the following steps: Step S41, obtaining an average excess carrier concentration value delta n 0 of the calibration area under specific light intensity according to the excess carrier concentration value delta n of the calibration area under different light intensity in step S2, and obtaining an average PL brightness value I PL , 0 of the calibration area under the same specific light intensity according to the spatially resolved photoluminescence PL brightness values of the whole silicon wafer sample under different light intensity in step S3; Step S42, according to Deltan 0 and I PL , 0 , calculating to obtain a calibration constant C through the following formula: Wherein I PL,0 is the average PL luminance value of the calibration region at a specific light intensity, Δn 0 is the average excess carrier concentration value of the calibration region at the same specific light intensity, C is the calibration constant, and N doped is the doping concentration of the single crystal silicon substrate.
7. The method for testing surface recombination of crystalline silicon according to claim 1, wherein the step S5 specifically comprises the following steps: step S51, when any point in the silicon wafer sample corresponds to a pixel point with x abscissa and y ordinate in a pixel matrix of a camera of the PL equipment, under the condition that the light intensity is n sun, the spatially resolved photoluminescence PL brightness value of the point with (x, y) coordinate is I PL_n (x, y); Step S52, according to I PL_n (x, y) and a calibration constant C, obtaining a spatial resolution excess carrier concentration value delta n _n (x, y) of a point with coordinates (x, y) in a silicon wafer sample under the same light intensity through the following formula: Wherein I PL_n (x, y) is the spatially resolved photoluminescence PL brightness value of the point with the coordinates of (x, y) in the silicon wafer sample under the light intensity of N sun, delta N _n (x, y) is the spatially resolved excess carrier concentration value of the point with the coordinates of (x, y) in the silicon wafer sample under the same light intensity, C is a calibration constant, and N doped is the doping concentration of the monocrystalline silicon substrate.
8. The method according to claim 7, wherein in the step S6, according to Δn _n (x, y) and the calibration constant C, the spatially resolved minority carrier lifetime τ eff (x, y) of the point with coordinates (x, y) in the silicon wafer sample under the same light intensity is obtained by the following formula: Wherein Deltan _n (x, y) is the spatial resolution excess carrier concentration value of a point with coordinates (x, y) in a silicon wafer sample under n solar light intensities, tau eff (x, y) is the spatial resolution minority carrier lifetime of the point with coordinates (x, y) in the silicon wafer sample under the same light intensity, R is the reflectivity of the silicon wafer sample, W is the thickness of a monocrystalline silicon substrate, phi is the photon flux irradiated to the surface of the silicon wafer sample by PL equipment, and the photon flux of 1 solar light intensity is 2.5X10 17 cm -2 s -1 .
9. The method according to claim 8, wherein in the step S7, the spatially resolved surface recombination value J 0 (x, y) of the point with coordinates (x, y) in the silicon wafer sample at the specific implantation concentration is obtained by the following formula: Wherein solar light intensity n is greater than solar light intensity m, deltan _n (x, y) is a spatially resolved excess carrier concentration value under n solar light intensities, deltan _m (x, y) is a spatially resolved excess carrier concentration value under m solar light intensities, tau cor_n (x, y) is a corrected minority carrier lifetime under n solar light intensities, tau cor_m (x, y) is a corrected minority carrier lifetime under m solar light intensities, q is a unit charge amount of a silicon wafer sample, the size is 1.6X10 -19 C, W is the thickness of a monocrystalline silicon substrate, n i is an intrinsic carrier concentration of the silicon wafer sample, and the size is 8.6X10 9 cm -3 .

Description

Test method for surface recombination of crystalline silicon Technical Field The invention relates to the technical field of solar cells, in particular to a testing method for surface recombination of crystalline silicon. Background The magnitude of the surface recombination value of crystalline silicon (simply referred to as a silicon wafer) has a direct connection with the open-circuit voltage of the crystalline silicon solar cell, so in order to ensure a higher open-circuit voltage, passivation antireflection films are generally deposited on the front surface and the rear surface of the crystalline silicon solar cell to reduce the surface recombination of the crystalline silicon. The surface recombination of crystalline silicon is usually obtained by WCT-120 minority carrier lifetime test of Sinton company in the United states, namely, the change of photoconduction in the silicon chip is measured by an oscillator circuit coil, and then the electrical parameters such as minority carrier lifetime and surface recombination of the silicon chip under different injection concentrations (namely, the excessive carrier concentrations under different light intensities) are obtained. The size of the diameter of the oscillator circuit coil in the WCT-120 minority carrier lifetime test is 4cm, which means that the spatial resolution limit of the test is a circle with the diameter of 4cm, a silicon wafer sample with the diameter of less than 4cm cannot be tested by the WCT-120 minority carrier lifetime test, and the surface recombination value of the WCT-120 minority carrier lifetime test is an average value and cannot reflect the abnormal value of the local structure with the diameter of less than 4 cm. In the previous years, the commercialized crystalline silicon solar cell has single type, such as an aluminum back surface field cell and a PERC cell, the conversion efficiency of the crystalline silicon solar cell is low (< 23%), and the emitter of the crystalline silicon solar cell is uniformly doped on the whole surface, so that the WCT-120 minority carrier lifetime can be used for testing the surface recombination value of the silicon wafer. However, in recent years, as new structures are applied to crystalline silicon solar cells, such as selective emitter technology (SE) and local passivation contact technology, the efficiency of commercial crystalline silicon solar cells gradually breaks through to 24% and above, and in the new commercial crystalline silicon solar cells generated therewith, the electrical properties of the local structures of the silicon wafer and the structures in the rest are significantly different, the surface recombination values of the local structures of the silicon wafer and the structures in the rest are also significantly different, the size of the local structures of the silicon wafer is usually in a micrometer scale, such as the local heavily doped regions in the SE structure, the width of the local heavily doped regions is typically 80-120 μm, the diameter is far smaller than 4cm, and the surface recombination values of the local structures of the silicon wafer cannot be tested by using the WCT-120 minority carrier lifetime. Under the situation, the method generally adopted in the industry is to prepare a large-area test area with the same performance as that of the local structure on a silicon wafer, enable the area of the test area to reach the size of a 4cm diameter circle, then test the surface recombination value of the test area by adopting WCT-120 minority carrier lifetime, but the large-area test area has a plurality of defects that 1) the performance of the large-area test area and the performance of the small-size local structure are difficult to be completely the same, namely the surface recombination value obtained by the large-area test area cannot accurately represent the surface recombination value of the small-size local structure. Taking laser SE as an example, if the laser is used for continuously scanning the silicon wafer for doping, a test area with the side length of 4cm is formed, the laser can undergo multiple acceleration, deceleration and translation movements within the range of the test area with the side length of 4cm, and the accuracy of the surface recombination value of the small-size local structure of the silicon wafer can be greatly influenced as compared with the movement of the laser in the preparation of an actual laser SE battery. 2) The preparation time of the large-area test area is long. Taking laser SE as an example, the time to form a test area with a side length of 4cm is 200 times or more the time required in actual laser SE cell production. Besides the defects of insufficient accuracy and long time consumption, the efficiency of process debugging on a single silicon wafer is extremely low due to the limited number of large-area test areas which can be accommodated on the single silicon wafer. Taking laser SE as an example, when laser p