Stacked photovoltaic device

Abstract

A stacked photovoltaic device comprises at least three p-i-n junction constituent devices superposed in layers, each having a p-type layer, an i-type layer and an n-type layer which are formed of silicon type non-single-crystal semiconductors. An amorphous silicon layer is used as the i-type layer of a first p-i-n junction, a microcrystalline silicon layer is used as the i-type layer of a second p-i-n junction and a microcrystalline silicon layer is used as the i-type layer of a third p-i-n junction, the first to third layers being in the order from the light-incident side. A stacked photovoltaic device can be provided which is practicable and low-cost and yet has a high reliability, and also has a high photoelectric conversion efficiency.

What is claimed is:  
     
         1 . A stacked photovoltaic device comprising at least three p-i-n junction constituent devices superposed in layers, each having a p-type layer, an i-type layer and an n-type layer which are formed of silicon type non-single crystal semiconductors, wherein; 
 an amorphous silicon layer is used as the i-type layer of a first p-i-n junction, a microcrystalline silicon layer is used as the i-type layer of a second p-i-n junction and a microcrystalline silicon layer is used as the i-type layer of a third p-i-n junction; the first to third p-i-n junction layers being in the order from the light-incident side.    
     
     
         2 . The stacked photovoltaic device according to  claim 1 , wherein the microcrystalline silicon layer which is the i-type layer of the second p-i-n junction has a layer thickness in the range of from 0.5 μm to 1.5 μm.  
     
     
         3 . The stacked photovoltaic device according to  claim 1 , wherein the microcrystalline silicon layer which is the i-type layer of the third p-i-n junction has a layer thickness in the range of from 1.5 μm to 3.5 μm.  
     
     
         4 . The stacked photovoltaic device according to  claim 1 , wherein the microcrystalline silicon layer which is the i-type layer of the second p-i-n junction contains boron, and the boron is in a content not more than 8 ppm.  
     
     
         5 . The stacked photovoltaic device according to  claim 1 , wherein the microcrystalline silicon layer which is the i-type layer of the third p-i-n junction contains boron, and the boron is in a content not more than 8 ppm.  
     
     
         6 . The stacked photovoltaic device according to  claim 1 , wherein the n-type layer of the second p-i-n junction comprises microcrystalline silicon.  
     
     
         7 . The stacked photovoltaic device according to  claim 1 , wherein the n-type layer of the second p-i-n junction comprises a double layer consisting of a microcrystalline silicon layer and an amorphous silicon layer.  
     
     
         8 . The stacked photovoltaic device according to  claim 1 , wherein the n-type layer of the third p-i-n junction comprises microcrystalline silicon.  
     
     
         9 . The stacked photovoltaic device according to  claim 1 , wherein the n-type layer of the third p-i-n junction comprises a double layer consisting of a microcrystalline silicon layer and an amorphous silicon layer.  
     
     
         10 . The stacked photovoltaic device according to  claim 1 , wherein the microcrystalline silicon layers which are the i-type layers of the second and third p-i-n junctions each have an optical absorption coefficient of 200 cm −1  or above at 950 nm.  
     
     
         11 . The stacked photovoltaic device according to  claim 1 , wherein the microcrystalline silicon layer which is the i-type layer of the second p-i-n junction is formed by plasma chemical vapor deposition using a high frequency power of from 0.1 GHz to 10 GHz.  
     
     
         12 . The stacked photovoltaic device according to  claim 1 , wherein the microcrystalline silicon layer which is the i-type layer of the third p-i-n junction is formed by plasma chemical vapor deposition using a high frequency power of from 0.1 GHz to 10 GHz.  
     
     
         13 . The stacked photovoltaic device according to  claim 1 , which is formed by a roll-to-roll system in which the layers are superposed while transporting a continuous substrate stretched over a pair of rolls.