Homogeneous dispersion of organic $p$-dopants in an organic semiconductor as an origin of high charge generation efficiency

We report that an organic $p$-dopant tri[1,2-bis(trifluoromethyl)ethane-1,2-dithiolene] $[Mo(tfd)3]$ resulted in higher density of holes than inorganic metal oxide dopants of $ReO3$ or $MoO3$ in 1,4-bis[N-(1-naphthyl)-$N′$-phenylamino]-$4,4′$-diamine even though the metal oxide dopants possess deeper work functions compared to $Mo(tfd)3$⁠. Higher charge generation efficiency results largely from the homogeneous dispersion of $Mo(tfd)3$ in the host. In contradistinction, the transmission electron microscopy analysis revealed a formation of metal oxide nanoclusters. This highlights the importance of homogeneous dispersion for an efficient doping.