Aromatic polyimide film, laminate, and solar cell

Abstract

A CIS solar cell having flexibility and high conversion efficiency may be produced, using, as a substrate, a polyimide film which is prepared from an aromatic tetracarboxylic acid component comprising 3,3′,4,4′-biphenyltetracarboxylic dianhydride as the main component and an aromatic diamine component comprising p-phenylenediamine as the main component, and has a maximum dimensional change in the temperature-increasing step of from 25° C. to 500° C. within a range of from +0.6% to +0.9%, excluding +0.6%, based on the dimension at 25° C. before heat treatment.

1 . A polyimide film prepared from an aromatic tetracarboxylic acid component comprising 3,3′,4,4′-biphenyltetracarboxylic dianhydride as the main component and an aromatic diamine component comprising p-phenylenediamine as the main component; wherein
 the polyimide film has a maximum dimensional change in the temperature-increasing step of from 25° C. to 500° C. within a range of from +0.6% to +0.9%, excluding +0.6%, based on the dimension at 25° C. before heat treatment. 
 
     
     
         2 . A polyimide film as claimed in  claim 1 , wherein the polyimide film has a weight loss after heat treatment at 500° C. for 20 min within a range equal to or less than 1 wt %. 
     
     
         3 . A polyimide film as claimed in  claim 1 , wherein the polyimide film has a coefficient of thermal expansion from 25° C. to 500° C. within a range of from 10 ppm/° C. to 20 ppm/° C., excluding 10 ppm/° C. 
     
     
         4 . A polyimide film as claimed in  claim 1 , wherein the polyimide film has a thickness within a range of from 7.5 μm to 75 μm. 
     
     
         5 . A laminate comprising a polyimide film as claimed in  claim 1 , and a metal layer which is formed on or over the polyimide film. 
     
     
         6 . A laminate as claimed in  claim 5 , wherein the metal layer comprises molybdenum. 
     
     
         7 . A laminate as claimed in  claim 5 , wherein the metal layer is formed by sputtering or vapor deposition. 
     
     
         8 . A CIS solar cell comprising a polyimide film as claimed in  claim 1  as a substrate, and further comprising at least a conductive metal layer and a chalcopyrite semiconductor layer on or over the substrate. 
     
     
         9 . A process for producing a polyimide film by thermal imidization, comprising:
 a step of reacting an aromatic tetracarboxylic acid component comprising 3,3′,4,4′-biphenyltetracarboxylic dianhydride as the main component and an aromatic diamine component comprising p-phenylenediamine as the main component in a solvent to provide a polyimide precursor solution;   a step of flow-casting the obtained polyimide precursor solution on a support, and heating the solution to form a self-supporting film, that is, casting step; and   a step of heating the obtained self-supporting film to conduct the imidization reaction, that is, curing step;   
       wherein
 the self-supporting film prepared in the casting step has a weight loss within a range of from 36% to 39%, this weight loss being calculated by the following formula (A):
   Weight loss(%)=( W 1 −W 2)/ W 1×100  (A)
 
 
 
       wherein W1 represents the weight of the self-supporting film, and W2 represents the weight of the polyimide film after curing; and
 in the casting step, the highest temperature (T1) is equal to or lower than the temperature (T M ) at which the self-supporting film is thermally deformed; and 
 in the curing step, the self-supporting film is heated at a temperature lower than the heat deformation temperature (T M ), and then the temperature is increased and the film is heated at the highest heat treatment temperature (T2) of from 470° C. to 540° C. 
 
     
     
         10 . A process for producing a polyimide film as claimed in  claim 9 , wherein the polyimide film produced has a thickness within a range of from 7.5 μm to 75 μm. 
     
     
         11 . A process for producing a polyimide film as claimed in  claim 9 , wherein in the casting step, the highest temperature (T1) is equal to or lower than 140° C. 
     
     
         12 . A process for producing a laminate, comprising steps of:
 producing a polyimide film according to a production process as claimed in  claim 9 ; and   forming a metal layer on the surface of the polyimide film.   
     
     
         13 . A process for producing a CIS solar cell, comprising steps of:
 producing a polyimide film according to a production process as claimed in  claim 9 ;   forming a metal layer on the surface of the polyimide film;   forming a chalcopyrite semiconductor layer on or over the metal layer; and   heating at a temperature equal to or higher than 450° C.