A density functional theory study on the degradation mechanism of thin film of organic semiconductor by water molecules

Hybrid density functional theory calculations have been carried out for the organic–inorganic hybrid complex of 1,4,5,8-naphthalene-tetracarboxylic-dianhydride (NTCDA) with an indium atom (In) to elucidate the degradation mechanism of thin films of molecular organic semiconductors by water molecules. This compound has been used as an organic semiconductor. The band gap of NTCDA was calculated to be as high as 3.39 eV as a single molecule, whereas a new band of NTCDA was formed as low-lying excited state (1.64 eV) after the interaction with the In atom. The water molecule attacked preferentially the In atom of In-NTCDA, and the solvation structure was formed around the In atom (solvation). Further addition of a water molecule to the system, the In atom is stripped off from NTCDA by water molecules, and solvation shell around the In atom is formed (separated solvation). The hydrogen-bond network was broken by the formation of solvation shell. The mechanism of degradation of the electron conductivity has been discussed on the basis of theoretical results.