DOUBLE-SIDED PASSIVATED CONTACT CELL AND MANUFACTURING METHOD THEREOF

Abstract

A method for producing a double-sided passivated contact cell, comprising the following steps: producing a tunnel layer on both the front and back sides of a silicon wafer after surface texturing of the silicon wafer; then producing a carbon-doped polysilicon layer on both the front and back sides of the silicon wafer by plasma-enhanced chemical vapor deposition (PECVD) or low-pressure chemical vapor deposition (LPCVD), wherein methane is used as the carbon source for carbon doping, and wherein the carbon doping content in the carbon-doped polysilicon layer is 1% to 5%; subsequently performing boron doping on one of the front-side and back-side polysilicon layers and phosphorus doping on the other polysilicon layer.Then, a passivation layer is produced on both the front and back sides of the silicon wafer, followed by the printing of electrodes on both the front and back sides of the silicon wafer, wherein the use of methane as a carbon source also increases the hydrogen content of the passivation interface and improves the passivation effect, wherein the band gap width of the carbon-doped polysilicon layer is increased by carbon doping, wherein the carbon-doped polysilicon layer with the increased band gap is used as the passivation material for the front and back sides of the silicon wafer, which reduces the absorption loss caused by parasitic absorption in the infrared and improves the cell current, thereby significantly improving the efficiency of the solar cell.

Description

TECHNICAL FIELDThe present invention relates to the field of photovoltaics, in particular to a double-sided passivated contact cell and a production method thereof.PRIOR ARTThe tunnel oxide passivation contact (TOPCon) is a passivation structure for crystalline silicon solar cells, which is made of an ultra-thin layer of silicon oxide and a layer of heavily doped polycrystalline silicon and is mainly used for passivation of the back side of the cell, whereby excellent surface passivation and selective collection of charge carriers can be achieved. However, the front side of this cell is still a metal-semiconductor contact and the composite loss at the metal-semiconductor contact pad limits the further improvement in cell efficiency. In order to further improve the conversion efficiency of the cell, the front side of the cell also needs to have a passivation contact structure. However, the front surface of the cell should have not only excellent passivation capability but also good optical transmissivity to avoid the efficiency loss caused by parasitic absorption.US 2020 / 0 075 789 A1 discloses a solar cell with a photoelectric heterojunction device and methods for producing the same.CONTENT OF THE PRESENT INVENTIONTechnical ProblemSolution of the ProblemTechnical SolutionAn object of the present invention is to provide a double-side passivated contact cell and a manufacturing method thereof, wherein by modifying poly through co-doping of elements, the band gap width of poly is increased, thereby improving the light transmittance of the passivation layer while ensuring passivation performance and improving current.To achieve the above object, the present invention provides a double-side passivated contact cell, wherein front and back surfaces of the double-side passivated contact cell are provided with a tunnel layer, a doped polysilicon layer and a passivation layer from inside to outside, respectively, and one of the doped polysilicon layers on the front and back surfaces is a polysilicon layer co-doped with boron and carbon and the other is a polysilicon layer co-doped with phosphorus and carbon.Preferably, the tunnel layer is an ultra-thin oxide layer.Preferably, the ultra-thin oxide layer is an alumina layer or a silica layer.Preferably, the ultra-thin oxide layer has a thickness of 0.5 to 2.5 nm (preferably 1 to 2 nm).Preferably, the content of carbon doping in the doped polysilicon layer is 1% to 5% (preferably 3% to 4%).The passivation layer is preferably an SiNx layer.The present invention further provides a method for manufacturing a double-side passivated contact cell, comprising the steps of: forming a tunnel layer on each of the front side and the back side of the silicon wafer after surface texturing of the silicon wafer, then forming a carbon doped polysilicon layer on each of the front side and the back side of the silicon wafer, then performing boron doping on one of the front side polysilicon layer and the back side polysilicon layer and phosphorus doping on the other, then forming a passivation layer on each of the front side and the back side of the silicon wafer, then printing electrodes on each of the front side and the back side of the silicon wafer.Preferably, the carbon doped polysilicon layer is formed by plasma enhanced chemical vapor deposition (PECVD) or low pressure chemical vapor deposition (LPCVD).In the case of carbon doping, methane (CH 4) is preferably used as carbon source.Preferably, the silicon wafer is an N-type wafer; wherein the front side polysilicon layer is boron doped and the back side polysilicon layer is phosphorus doped; and wherein the fabricated double side passivated contact cell is an N-type double side passivated contact cell.Advantageous Effect of the InventionAdvantageous EffectThe present invention has advantages and advantageous effects as follows: the present invention provides a double-side passivated contact cell and a manufacturing method thereof, in which in the present invention, by modifying poly through co-doping of elements, the band gap width of the polysilicon layer is increased, thereby improving the light transmittance of the passivation layer while ensuring the passivation performance, and improving the current.The present invention adopts the passivation contact structure of the double-side co-doped passivation layer and the tunnel layer, which can greatly reduce the carrier composite on the surface of the cell and increase the open circuit voltage of the cell; and using CH 4 as a carbon source also increases the H content of the passivation interface and improves the passivation effect, and maximum implicit open circuit voltage (Ivoc) can reach 750 mV; and the band gap width of the polysilicon layer is increased by carbon doping, the modified wide band gap poly is used as a passivation material for the front side and the back side, which reduces the absorption loss caused by parasitic infrared and improves the cell current, thereby significantly improving the efficiency of the solar cell.The present invention controls the thickness of the ultra-thin oxide film to 0.5 to 2.5 nm, preferably 1 to 2 nm, in order to prevent the ultra-thin oxide film from being too thin or too thick; if the ultra-thin oxide film is too thin, the passivation effect is weak; and if the ultra-thin oxide film is too thick, the tunnel effect is deteriorated, which deteriorates the passivation effect.The present invention controls the content of carbon doping in the polysilicon layer to 1% to 5%, preferably 3% to 4%, in order to avoid the carbon doping content being too small or too large; if the carbon doping content is too small, the increase in the band gap width of the polysilicon layer will be small, and the passivation and the current increase will be small; if the carbon doping content is too large, the contact resistance is deteriorated, thereby reducing FF.For carbon doping, the present invention may adopt a PECVD or LPCVD process using methane (CH 4) as carbon source, whereupon high temperature pastes may be printed, or indium tin oxide (ITO) and low temperature pastes may be used to reduce the cross resistance and increase fill factor (FF).DETAILED DESCRIPTIONBest Modes for Implementing the Present Invention and Best Modes for Implementing the Present InventionIn connection with embodiments, the detailed embodiments of the present invention will be explained in more detail below. The following embodiments serve to more clearly explain the technical solution of the present invention, but the scope of the present invention is not limited thereto.The present invention provides an N-type double-side passivated contact cell, wherein front and back surfaces of the double-side passivated contact cell are provided with a tunnel layer, a doped polysilicon layer and a passivation layer from the inside to the outside, respectively, one after another;and wherein the tunnel layer is an ultra-thin oxide layer which may take an alumina layer or a silicon dioxide layer, and wherein the ultra-thin oxide layer has a thickness of 0.5 to 2.5 nm (preferably 1 to 2 nm);and wherein the content of carbon doping in the doped polysilicon layer is 1% to 5% (preferably 3% to 4%);and wherein the doped polysilicon layer on the front side is a polysilicon layer co-doped with boron and carbon;and wherein the doped polysilicon layer on the back side is a polysilicon layer co-doped with phosphorus and carbon;and wherein the passivation layer is a SiNx layer.The present invention further provides a method of manufacturing an N-type double-side passivated contact cell, comprising the steps of: forming a tunnel layer on each of the front and back surfaces of the silicon wafer after surface texturing of the N-type silicon wafer; then forming a carbon doped polysilicon layer on each of the front and back surfaces of the silicon wafer; subsequently performing boron doping on the front surface polysilicon layer and phosphorus doping on the back surface polysilicon layer; then forming a passivation layer on each of the front and back surfaces of the silicon wafer; subsequently printing electrodes on each of the front and back surfaces of the silicon wafer.More specifically, the carbon doped polysilicon layer may be formed by plasma enhanced chemical vapor deposition (PECVD) or low pressure chemical vapor deposition (LPCVD), and methane (CH 4) may be used as a carbon source in carbon doping.Specific embodiments of the present invention are as follows:Embodiment 1forming silicon oxide having a thickness of 1.2 nm on each of the front and back surfaces of the silicon wafer as a tunnel layer after surface texturing of the N-type silicon wafer; then forming a carbon doped polysilicon layer on each of the front and back surfaces of the silicon wafer, the content of carbon doping in the polysilicon layer being 1%; subsequently performing boron doping on the front surface polysilicon layer and phosphorus doping on the back surface polysilicon layer; then forming a SiNxlayer as a passivation layer on each of the front and back surfaces of the silicon wafer; subsequently printing electrodes on each of the front and back surfaces of the silicon wafer; and finally, an N-type double-side passivated contact cell is formed.Embodiment 2forming silicon oxide having a thickness of 1.2 nm on each of the front and back surfaces of the silicon wafer as a tunnel layer after surface texturing of the N-type silicon wafer; then forming a carbon doped polysilicon layer on each of the front and back surfaces of the silicon wafer, the content of carbon doping in the polysilicon layer being 3%; subsequently performing boron doping on the front surface polysilicon layer and phosphorus doping on the back surface polysilicon layer; then forming a SiNxlayer as a passivation layer on each of the front and back surfaces of the silicon wafer; subsequently printing electrodes on each of the front and back surfaces of the silicon wafer; and finally, an N-type double-side passivated contact cell is formed.Embodiment 3forming silicon oxide having a thickness of 1.2 nm on each of the front and back surfaces of the silicon wafer as a tunnel layer after surface texturing of the N-type silicon wafer; then forming a carbon doped polysilicon layer on each of the front and back surfaces of the silicon wafer, the content of carbon doping in the polysilicon layer being 10%; subsequently performing boron doping on the front surface polysilicon layer and phosphorus doping on the back surface polysilicon layer; then forming a SiNxlayer as a passivation layer on each of the front and back surfaces of the silicon wafer; subsequently printing electrodes on each of the front and back surfaces of the silicon wafer; and finally, an N-type double-side passivated contact cell is formed.Comparative Example 1Performing boron doping on the front side of the silicon wafer after surface texturing of the N-type silicon wafer, forming silicon oxide having a thickness of 1.2 nm on the back side of the silicon wafer as a tunnel layer; subsequently depositing a polysilicon layer on the silicon oxide and performing phosphorus doping on the back side polysilicon layer; then forming a SiNxlayer as a passivation layer on the front side and the back side of the silicon wafer, respectively; subsequently printing electrodes on the front side and the back side of the silicon wafer, respectively; and finally, a double-side passivated N-type contact cell is formed.The performance of the N-type double-side passivated contact cells manufactured by each of the embodiments and the comparative ratio 1 is tested, and the performance data of the respective embodiments are compared with those of the comparative example 1; using the performance data of the comparative example 1 as the basis for the comparison, the differences between the performance data of the embodiments and the performance data of the comparative example 1 are shown in the following table:Comparative Example 1----Embodiment 16- 0,30,20,1Embodiment 271,10,10,4Embodiment 331,5- 1,10,1From the above comparisons, the following is apparent:As compared with Comparative Example 1, in Embodiment 1, a tunnel oxide film and an overlying boron- and carbon-co-doped polysilicon film are deposited on the front surface of the silicon wafer to serve as a passivation film, the content of carbon doping is 1%; the tunnel oxide film and the overlying boron- and carbon-co-doped polysilicon film on the front surface of the silicon wafer can effectively improve the open circuit voltage and the fill factor, but due to a low content of carbon doping, the loss of the current density is larger, and the overall improvement of the efficiency of the cell is not obvious.As compared with Comparative Example 1, in Embodiment 2, a tunnel oxide film and an overlying boron- and carbon-co-doped polysilicon film are deposited on the front surface of the silicon wafer to serve as a passivation film, the content of carbon doping is 3%; the tunnel oxide film and the overlying boron- and carbon-co-doped polysilicon film on the front surface of the silicon wafer can improve open circuit voltage, the content of carbon doping is appropriate, the current density also increases, and the efficiency of the cell is greatly improved.As compared with Comparative Example 1, in Embodiment 3, a tunnel oxide film and an overlying boron- and carbon-co-doped polysilicon film are deposited on the front surface of the silicon wafer to serve as a passivation film, the content of carbon doping is 10%; the tunnel oxide film and the overlying boron- and carbon-co-doped polysilicon film on the front surface of the silicon wafer can effectively improve the open circuit voltage and the current density, but due to too high a content of carbon doping, the cross resistance is increased and FF is greatly reduced, and the improvement of the efficiency of the cell is not obvious.In summary, in the present invention, as compared with Comparative Example 1, a tunnel oxide layer and an overlying boron- and carbon-co-doped polysilicon layer on the front side of the silicon wafer serve as a passivation layer, and at the same time, the phosphorus-doped poly on the back side of the silicon wafer is also carbon-doped; the tunnel oxide layer and the overlying boron- and carbon-co-doped polysilicon layer on the front side of the silicon wafer can effectively passivated the defects in the contact region, thereby significantly improving Voc and FF; at the same time, the carbon doping also reduces the absorption of light by the poly and increases the current, which in turn significantly improves the efficiency of the cell.

Claims

A method of manufacturing a double-side passivated contact cell, comprising the steps of: forming a tunnel layer on each of the front and back surfaces of a silicon wafer after surface texturing of the silicon wafer, then forming a carbon doped polysilicon layer on each of the front and back surfaces of the silicon wafer by plasma enhanced chemical vapor deposition (PECVD) or low pressure chemical vapor deposition (LPCVD), wherein the carbon doping uses methane as a carbon source, wherein the content of carbon doping in the carbon doped polysilicon layer is 1% to 5%, then performing boron doping on one of the front and back polysilicon layers and phosphorus doping on the other polysilicon layer, then forming a passivation layer on each of the front and back surfaces of the silicon wafer, subsequently printing electrodes on the front and back surfaces of the silicon wafer, respectively, using methane as a carbon source also increases the hydrogen content of the passivation interface and improves the passivation effect, increasing the band gap width of the carbon doped polysilicon layer by carbon doping, using the carbon doped polysilicon layer with increased band gap as a passivation material for the front and back surfaces of the silicon wafer, reducing the absorption loss caused by parasitic absorption in the infrared and improving the cell current, thereby significantly improving the efficiency of the solar cell.Method for producing a double-sided passivated contact cell according to Claim 1, characterized in that the tunnel layer is an ultra-thin oxide layer.Method for producing a double-sided passivated contact cell according to claim 2, characterised in that the ultra-thin oxide layer is an aluminium oxide layer or a silicon dioxide layer.The method for manufacturing a double-side passivated contact cell according to claim 2, characterized in that the ultra-thin oxide layer has a thickness of 0.5 to 2.5 nm.Method for producing a double-sidedly passivated contact cell according to Claim 1, characterized in that the passivation layer is an SiNx layer.The method for manufacturing a double-side passivated contact cell according to claim 1, characterized in that the silicon wafer is an N-type wafer; wherein the front side polysilicon layer is boron doped and the back side polysilicon layer is phosphorus doped; and wherein the manufactured double-side passivated contact cell is an N-type double-side passivated contact cell.