Based on spin coating in humidity controlled environment an extremely simple deposition process is established which allows convenient and reproducible coating of photomultiplier tubes (PMTs) to achieve an improvement in photon sensitivity and thereby a higher quantum efficiency. The coatings consisting of a blend of polyacrylate based copolymer with p-terphenyl are obtained from dichloromethane solutions. On the curved PMTs structures due to crystallization of p-terphenyl superposed with pores in the copolymer matrix are present. On flat substrates coatings established under identical conditions exhibit the same porous structure. The origin of the obtained structures is discussed in context of breath figures.