Process for making an organic charge transporting film

A method of making an organic charge transporting film;

• said method comprising steps of:
• (a) coating on a surface a formulation comprising:
• (i) a polymer having Mn at least 4,000 and comprising polymerized units of a compound of formula NAr1Ar2Ar3, wherein Ar1, Ar2 and Ar3 independently are C6-C50 aromatic substituents and at least one of Ar1, Ar2 and Ar3 contains a vinyl group attached to an aromatic ring, provided that said compound has no arylmethoxy linkages;
• (ii) an acid catalyst
• which
• is an organic Bronsted acid with pKa≤4;
• a Lewis acid comprising a positive aromatic ion and an anion which is (i) a tetraaryl borate having the formula
• wherein R represents zero to five non-hydrogen substituents selected from D, F and CF3, (ii) BF4−, (iii) PF6−, (iv) SbF6−, (v) AsF6− or (vi) ClO4−;
• or a thermal acid generator which is an ammonium or pyridinium salt of an organic Bronsted acid with pKa≤2 or an ester of an organic sulfonic acid;
• and (iii) a solvent;
• and (b) heating the coated surface to a temperature from 120 to 280° C.