The Formula (1) was derived from small-signal admittance of the system carrying single-charge-space-charge-limited current (SCSCLC). The admittance was presented by Shao and Wright in . To get Formula (1) the following conditions:equation(3)d(ωCo-Y″)dω=0should be applied to susceptance (Y″).
To estimate μ on the basis of (1), particular conditions should be executed. Firstly the Eq. (1) P 22077 valid when SCSCLC flows in an organic layer. It requires an ohmic electrode at one side and an electrode well collecting charges at the other side. Secondly the Formula (1) deals with trap-free case. A direct current takes then the form:equation(4)jo=98εoεμVo2d3,
where εo is the vacuum permittivity and ε is the dielectric constant of organic material. In spite of rather strong requirements, the small-signal-admittance method (SSAM) referring to (1) is often applied to estimate μ. For instance, this method enabled to study hole and electron mobility in poly dialkoxy-p-phenylene vinylene (PPV) , hole mobility in N,N′-diphenyl-N,N′-bis(1-naphthyl)(1,1′-biphenyl)-4,4′-diamine (NPB) , hole and electron mobilities in tris(8-hydroxy-quinolinato)aluminium (Alq3) .