Capping layers for improved crystallization

摘要

Techniques for fabrication of kesterite Cu—Zn—Sn—(Se,S) films and improved photovoltaic devices based on these films are provided. In one aspect, a method of fabricating a kesterite film having a formula Cu2−xZn1+ySn(S1−zSez)4+q, wherein 0≦x≦1; 0≦y≦1; 0≦z≦1; and −1≦q≦1 is provided. The method includes the following steps. A substrate is provided. A bulk precursor layer is formed on the substrate, the bulk precursor layer comprising Cu, Zn, Sn and at least one of S and Se. A capping layer is formed on the bulk precursor layer, the capping layer comprising at least one of Sn, S and Se. The bulk precursor layer and the capping layer are annealed under conditions sufficient to produce the kesterite film having values of x, y, z and q for any given part of the film that deviate from average values of x, y, z and q throughout the film by less than 20 percent.

主权项

1. A method of fabricating a kesterite film having a formula Cu2−xZn1+ySn(S1−z Sez)4+q, wherein 0≦x≦1; 0≦y≦1; 0≦z≦1; and −1≦q≦1, the method comprising the steps of:
providing a substrate; forming a bulk precursor layer on the substrate, the bulk precursor layer comprising Cu, Zn, Sn and at least one of S and Se, wherein the bulk precursor layer is an only source of Cu and Zn in the kesterite film such that a composition of Cu and Zn in the kesterite film is determined by a composition of Cu and Zn in the bulk precursor layer; analyzing the bulk precursor layer formed on the substrate to determine a composition of the bulk precursor layer; forming a solid capping layer on the bulk precursor layer, the capping layer comprising at least one of Sn, S and Se, wherein the capping layer is configured to provide a source of additional elemental chalcogen at a surface of the kesterite film; and annealing the bulk precursor layer and the capping layer under conditions sufficient to produce the kesterite film having values of x, y, z and q for any given part of the film that deviate from average values of x, y, z and q throughout the film by less than 20 percent such that a composition of the kesterite film in terms of x, y, z and q is 0≦x≦1; 0≦y≦1; 0≦z≦1; and −1≦q≦1, wherein the capping layer serves to replace elements lost from the bulk precursor layer during the annealing step such that a composition and a thickness of the capping layer is based on the composition of the bulk precursor layer determined prior to forming the capping layer such that the kesterite film is produced having the formula Cu2−xZn1+ySn(S1−z Sez)4+q, wherein the capping layer is configured to provide a chalcogen-rich layer during the annealing step to control a grain size of the kesterite film, and a solid barrier on the bulk precursor layer to prevent elemental loss from the bulk precursor during the annealing step.