Thin-film solar cell

Abstract

The present invention relates to thin-film solar cells of the CIGS-type. A characteristic feature of the invention is the use of two integrally formed buffer layers, a first ALD Zn(O,S) buffer layer ( 7 ) on top of the CIGS-layer ( 3 ) and a second ALD ZnO-buffer layer ( 8 ) on top of the first ( 7 ) buffer layer. Both buffer layers are deposited in the same process step using ALD (atom layer deposition). The invention also relates to a method of producing the cell and a process line for manufacturing of the cell structure.

1 - 15 . (canceled)  
   
   
       16 . A thin-film solar cell comprising a thin film of p-type semiconductor Cu(In,Ga)(Se,S) 2  light absorbing layer (CIGS-layer) ( 3 ) formed on a back electrode layer ( 2 ), a thin film of transparent conductive metal oxide formed over the light absorbing layer, having n-type conductivity and serving as a window layer ( 5 ) and electrode, and an interfacial layer ( 6 ) between the window layer and the CIGS-layer characterized by said interfacial layer comprising a first sulphur containing buffer layer ( 7 ) ALD grown on the CIGS-layer, and a second buffer layer ( 8 ) integrally formed with the first buffer layer by ALD deposition and comprising ZnO.  
   
   
       17 . A thin-film solar cell in accordance with  claim 16  characterized in that the first buffer layer ( 7 ) is ALD deposited Zn(O x ,S 1-x ), where x varies between 0 and 0,9, preferably between 0,1 and 0,7  
   
   
       18 . A thin-film solar cell in accordance with  claim 16  characterized in that the first buffer layer ( 7 ) is ALD deposited In 2 S 3 .  
   
   
       19 . A thin-film solar cell in accordance with  claim 17  characterized in that the thickness of the first buffer layer ( 7 ) is larger than about 1 nm and less than about 30 nm.  
   
   
       20 . A thin-film solar cell in accordance with  claim 16 , characterized in that there is a graded transition of the first buffer layer ( 7 ) into the second buffer layer ( 8 ), the sulphur content of the first buffer layer gradually decreasing in a direction over its thickness.  
   
   
       21 . A method of forming an interfacial layer between a thin film of p-type semiconductor Cu(In,Ga)(Se,S) 2  light absorbing layer (CIGS-layer) ( 3 ) and a thin film of n-type conductive window layer ( 5 ) on a substrate of—a thin film solar cell structure, the method comprising the steps of vacuum deposition of the CIGS layer in a CIGS process chamber vacuum deposition of the CIGS layer in a CIGS process chamber ( 11 ), characterized by transporting the substrates with deposited CIGS layer to an ALD process chamber without exposing the substrates to the atmosphere, and transporting the substrates with deposited CIGS layer to an ALD process chamber without exposing the substrates to the atmosphere, and providing said interfacial layer in the ALD process chamber in the ALD process chamber initially by depositing a first sulphur containing buffer layer ( 6 ) on the surface of the CIGS-layer using atomic layer deposition (ALD) and finally depositing a second ZnO layer ( 8 ) on top of the first buffer layer ( 7 ) using atomic layer deposition (ALD).  
   
   
       22 . A method in accordance with  claim 21  characterized by forming the first and second buffer layers ( 7 ,  8 ) in one and the same ALD process chamber ( 13 ).  
   
   
       23 . A method in accordance with  claim 21  characterized by forming the first and second buffer layers in separate, but linked ALD process chambers ( 13 ,  15 ).  
   
   
       24 . A method in accordance with  claim 21  characterized by providing the first sulphur containing buffer layer ( 7 ) by exposing the absorbing layer ( 3 ) in the ALD reaction chamber ( 13 ) alternatively to pulses of a organo metallic zinc compound such as for example diethyl zinc or dimethyl zinc to form a zinc containing monolayer or to pulses of water and H 2 S so as to grow oxygen and sulphur on the zinc atoms in order to form a first monolayer which is adsorbed on top of the light absorbing layer ( 3 ), repeating said steps to grow additional sulphur containing monolayers layers on top of each other, and continuing this process until the first sulphur containing buffer layer ( 7 ) of a first predefined thickness is obtained.  
   
   
       25 . A method in accordance with  claim 24  characterized by providing pulses of H 2 S in a proportion of 10-100%, preferably in a proportion of 15-25%, and most preferred in a proportion of 10% to the total number water- and H 2 S pulses.  
   
   
       26 . A method in accordance with  claim 24  characterized by providing the second ZnO buffer layer ( 8 ) in the same manner as the first buffer ( 7 ) layer leaving out the pulses of H 2 S, by continuing to expose the first buffer layer in the ALD reaction chamber alternatively to gas pulses of an organo metallic zinc compound, such as for example diethyl zinc or dimethyl zinc, and pulses of water until the second ZnO buffer layer of a second predefined thickness is obtained.  
   
   
       27 . A method in accordance with  claim 26  characterized by successively decreasing said proportion of sulphur as said additional monolayers are grown so as to obtain a gradual transition of the first buffer layer ( 7 ) into the second buffer layer ( 8 ).  
   
   
       28 . A process line for manufacturing a solar cell structure comprising a thin film of p-type semiconductor Cu(In,Ga)(Se,S) 2  light absorbing layer (CIGS-layer) ( 3 ) formed on a back electrode layer ( 2 ), a thin film ( 5 ) of transparent conductive metal oxide formed over the light absorbing layer, having n-type conductivity and serving as a window layer and electrode, and an interfacial layer ( 6 ) between the window layer and the CIGS-layer, said process line comprising a vacuum deposition chamber ( 11 ) in which the CIGS layer is vacuum deposited on a substrate characterized by an ALD process chamber ( 13 ) for ALD deposition of said interfacial layer by first growing a first sulphur containing buffer layer ( 7 ) on the surface of the CIGS-layer using ALD deposition, and finally growing a second buffer layer ( 8 ) containing ZnO on top of the first buffer layer using ALD deposition, and a transport chamber ( 12 ) arranged between the vacuum deposition chamber and the ALD process chamber for transportation of solar film blanks from the vacuum deposition chamber to the ALD deposition chamber without exposing the blanks to the atmosphere and for cooling the solar film blanks from the CIGS deposition temperature to the ALD deposition temperature.  
   
   
       29 . A process line in accordance with  claim 28 , characterized by an additional ALD process chamber ( 15 ) connected to said one ALD process chamber ( 13 ), said first mentioned ALD process chamber ( 13 ) being used for the ALD deposition of the first buffer layer ( 7 ) and said additional ALD process chamber ( 15 ) being used for the ALD deposition of the second buffer layer ( 8 ).