tailieunhanh - Polymer Thin Films Part 4

Tham khảo tài liệu 'polymer thin films part 4', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 64 Polymer Thin Films regime. Obviously J L L peqF0 see Eq. 29 . Therefore ttr f1 2 where the half-rise time of TrEL t1 2 is defined as JR t1 2 . The space charge- limited regime If the space- charge limited SCL regime of hole s transport is realized an electric field strength F x t is determined by space charge of holes except of several nanometers next to the cathode where electron s charge is important in accord with the Poisson s equation. If the dispersive transport is finished t t R one can connect the current with the density of holes ph x t J x t ụ t exp - t t F x t ph x t . 30 Following to the work Many Rakavy 1962 hence neglecting any diffusion the density of holes next to the cathode can be written as the step- like function x1 t Ph 0 x t _sSo eM t J dx ổ x - x 31 0 Fig. 11. Time dependencies of the initial rise of recombination current calculated in SCL regime solid lines and in IL regime dashed lines . Dotted lines show how the delay time td is defined. The values of applied voltage are shown in the figure. where s is the relative dielectric constant and x1 t 2LlnỊ1 1 - M t F0 2L is the leading front position. One can include approximately the field- stimulated broadening of step- like leading front of the distribution 31 replacing the Dirak delta- function in this equation by Gaussian function 28 with x and SF t F x t instead of ụeqF0t and SF t F0 respectively. By the use of Eq. 30 one obtains Non-equilibrium charge transport in disordered organic films 65 J L t ee0 t 2eM t F L t exp - t t erfc L - X1 t 2 Sf t F L t t t1 32 F L t F 0 L t - e eSo J ph X t - p X tĩịdx where F 0 L t Fo 1 - M t F0 2L . L The time t1 is the transit time of holes it is defined as X1 t1 L . F0M t1 L . 33 Obviously t1 Many Rakavy 1962 because Li t uq if t1 teq . Eqs. 25 26 and 32 or Eq. 29 in the injection- limited regime yields approximate analytic description of initial rise of TrEL. One has to note that the effects of filling of deep .