A solar cell, comprising: a substrate; an emitter layer formed on a first surface of the substrate; a first insulating layer on the emitter layer, the first insulating layer including a first lower layer and a first upper layer on the first lower layer, the first insulating layer having a first opening through the first lower layer and the first upper layer, wherein the maximum width of the first opening at the first lower layer is greater than the maximum width of the first opening at the first upper layer, further comprising a first electrode in the first opening electrically and physically connected to the emitter layer through the first opening, wherein the first electrode is formed of a plating layer which comprises: a metal seed layer on the emitter layer, a diffusion barrier layer on the metal seed layer and a conductive layer on the diffusion barrier layer, the conductive layer having a copper layer on the diffusion barrier layer and a tin layer on the copper layer, wherein the first opening is formed in a shape of a line pattern extending across the first surface of the substrate and has at the first upper layer a substantially uniform width, wherein a width of the first opening at an upper portion of the first lower layer is greater than a width of the first opening at a lower portion of the first lower layer, wherein a width of the first opening at an upper portion of the first lower layer is greater than a width of the first opening at a lower portion of the first upper layer, wherein a width of the first electrode where the metal seed layer is in direct contact with the emitter layer is the same as a width of the first opening at the lower portion of the first lower layer, and wherein the width of the first opening at the lower portion of the first lower layer is greater than a width of the first opening at a lower portion of the first upper layer. a substrate; an emitter layer formed on a first surface of the substrate; a first insulating layer on the emitter layer, the first insulating layer including a first lower layer and a first upper layer on the first lower layer, the first insulating layer having a first opening through the first lower layer and the first upper layer, wherein the maximum width of the first opening at the first lower layer is greater than the maximum width of the first opening at the first upper layer, further comprising a first electrode in the first opening electrically and physically connected to the emitter layer through the first opening, wherein the first electrode is formed of a plating layer which comprises: a metal seed layer on the emitter layer, a diffusion barrier layer on the metal seed layer and a conductive layer on the diffusion barrier layer, the conductive layer having a copper layer on the diffusion barrier layer and a tin layer on the copper layer, wherein the first opening is formed in a shape of a line pattern extending across the first surface of the substrate and has at the first upper layer a substantially uniform width, wherein a width of the first opening at an upper portion of the first lower layer is greater than a width of the first opening at a lower portion of the first lower layer, wherein a width of the first opening at an upper portion of the first lower layer is greater than a width of the first opening at a lower portion of the first upper layer, wherein a width of the first electrode where the metal seed layer is in direct contact with the emitter layer is the same as a width of the first opening at the lower portion of the first lower layer, and wherein the width of the first opening at the lower portion of the first lower layer is greater than a width of the first opening at a lower portion of the first upper layer. a metal seed layer on the emitter layer, a diffusion barrier layer on the metal seed layer and a conductive layer on the diffusion barrier layer, the conductive layer having a copper layer on the diffusion barrier layer and a tin layer on the copper layer, wherein the first opening is formed in a shape of a line pattern extending across the first surface of the substrate and has at the first upper layer a substantially uniform width, wherein a width of the first opening at an upper portion of the first lower layer is greater than a width of the first opening at a lower portion of the first lower layer, wherein a width of the first opening at an upper portion of the first lower layer is greater than a width of the first opening at a lower portion of the first upper layer, wherein a width of the first electrode where the metal seed layer is in direct contact with the emitter layer is the same as a width of the first opening at the lower portion of the first lower layer, and wherein the width of the first opening at the lower portion of the first lower layer is greater than a width of the first opening at a lower portion of the first upper layer.