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EP-3343639-B1 - METHOD FOR PRODUCING A SOLAR CELL WITH HIGH PHOTOELECTRIC CONVERSION EFFICIENCY

EP3343639B1EP 3343639 B1EP3343639 B1EP 3343639B1EP-3343639-B1

Inventors

  • HASHIGAMI, HIROSHI
  • WATABE, TAKENORI
  • OHTSUKA, HIROYUKI
  • Mitta, Ryo

Dates

Publication Date
20260513
Application Date
20161107

Claims (2)

  1. A method for manufacturing a solar cell, comprising: forming a p-type region (102) having a p-conductive type on a first main surface of a crystal silicon substrate (101); forming an n-type region (103) which has an n-conductive type and in which maximum concentration of additive impurities for providing the n-conductive type in a substrate depth direction is equal to or higher than 5×10 18 atoms/cm 3 , on the first main surface; forming a first passivation film (104) so as to cover the p-type region and the n-type region; forming a second passivation film (105) on a second main surface which is a surface opposite to the first main surface so as to cover the second main surface; forming a reflective coat (109) on the first passivation film; forming a positive electrode (106) in contact with a surface of the p-type region; and forming a negative electrode (107) in contact with a surface of the n-type region, wherein at least part of the second main surface has the same conductive type and conductivity as a conductive type and conductivity in a bulk portion of the crystal silicon substrate, wherein the first passivation film and the second passivation film are formed with a compound containing aluminum oxide, and wherein forming the positive electrode and forming the negative electrode comprises: a sub-step of applying conductive paste on the first passivation film or the reflective coat; and a sub-step of performing heat treatment on the crystal silicon substrate, to which the conductive paste is applied, at 700°C or more and 890°C or less for 1 second or more and 10 minutes or less, and the conductive paste is an Ag paste.
  2. The method for manufacturing solar cell according to claim 1, further comprising: forming an antireflective coat (108) on the second passivation film (105).

Description

TECHNICAL FIELD The present invention relates to a method for manufacturing a solar cell with high photoelectric conversion efficiency. BACKGROUND ART As a method for improving photoelectric conversion efficiency of a crystal silicon solar cell, in recent years, a so-called back surface electrode type solar cell, in which no electrodes are provided on a light receiving surface to eliminate optical loss due to shadow of electrodes, has been widely studied. FIG. 10 is a cross-sectional schematic diagram illustrating a basic structure of the back surface electrode type solar cell. In FIG. 10, the light receiving surface faces downward in the drawing. In the back surface electrode type solar cell 1000, a p-type region 1002 in which additives for providing p-type conductivity are diffused in high concentration is formed, and an n-type region 1003 in which additives for providing n-type conductivity are diffused in high concentration is formed so as to be adjacent to the p-type region 1002, on a non-light receiving surface of a substrate 1001. The p-type region 1002 and the n-type region 1003, and a surface (the light receiving surface) opposite to the regions are respectively covered with passivation films 1004 and 1005 for reducing loss due to recombination of photo-excited carriers. A positive electrode 1006 and a negative electrode 1007 are formed so as to penetrate the passivation film 1004. Further, while not illustrated in FIG. 10, on the light receiving surface of the substrate 1001, texture having several microns of roughness is formed for optical confinement. Because there is no electrode on the light receiving surface of the back surface electrode type solar cell, it is necessary to make charge carriers which are mainly excited by short-wavelength light reach the back surface without being recombined. Actually, the surface of the substrate densely contains dangling bonds (silicon dangling bonds) which act as recombination centers of charge carriers. Thus, extremely high passivation performance is required for the passivation film 1005. By the way, the recombination rate of charge carriers is the sum of the bulk recombination rate in the crystal bulk and the surface recombination rate on the crystal surface. Typically, in crystal silicon, as additive impurity concentration (charge carrier concentration at room temperature) becomes higher, bulk recombination increases. This is because a crystal defect due to additive impurities and direct recombination in Auger process are largely caused as the carrier concentration becomes higher. Therefore, typically in a high concentration region such as the p-type region 1002 and the n-type region 1003, carrier recombination loss on the back surface is prevented by reducing maximum additive impurity concentration in a substrate depth direction to, for example, a first half of 1018 atoms/cm3 and covering the surface with an effective passivation film. Further, surface passivation has two elements of a chemical termination and an electrical field effect. The electrical field effect is to generate an electric field on the surface of the substrate by fixed charges incorporated in the passivation film and reduce charge carrier concentration in the vicinity of the surface, thereby reducing recombination on the surface. In the solar cell, silicon nitride having positive charges and aluminum oxide having negative charges are typically often used for electrical field effect type passivation. In principle, a passivation effect of the electrical field effect type passivation can be obtained regardless of a conductive type on the surface of the substrate to which the passivation is applied. However, if a film containing fixed charges having the same polarity as that of majority carriers on the surface of the substrate is applied and an electrode is formed on the same surface, it is known that minority carriers flow to an electrode having polarity opposite to that of an electrode to which the minority carriers should be normally collected, which reduces output of the solar cell. To address this problem, Patent Literature 1 discloses an example where an aluminum oxide film is formed on a surface of a p-type region of a back surface electrode type solar cell, silicon oxide is applied on a surface of an n-type region, and silicon nitride is applied on a light receiving surface. On the other hand, as a typical example of chemical termination type passivation, there is silicon oxide. While silicon oxide has positive charges, silicon oxide has lower density of fixed charges than that of typical silicon nitride by single to double digits depending on a manufacturing method, and has relatively low defect density at an interface with crystal silicon. Thus, silicon oxide is considered useful for both a p-type surface and an n-type surface. In an example disclosed in Non-Patent Literature 1 (Mulligan), silicon oxide is applied to both a light receiving surface and a back surface of a solar