Electron affinity and binding energy of excitons in disordered organic semiconductors. I. Simulation-assisted analysis of field-induced exciton dissociation experiments

Three-dimensional kinetic Monte Carlo simulations are used to investigate the sensitivity to material parameters of the photoluminescence efficiency curves that are obtained from field-induced dissociation (FID) experiments of devices that are based on disordered small-molecule organic semiconductors. The study contains a comparison with the results of a simplified one-dimensional Master Equation model [O. Rubel , ] and with two-dimensional simulation results. The error-function-like efficiency curves show a field sensitivity that is strongly determined by the average exciton binding energy, <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"> <a:msub> <a:mi>E</a:mi> <a:mrow> <a:mi>exc</a:mi> <a:mo>,</a:mo> <a:mi mathvariant="normal">b</a:mi> </a:mrow> </a:msub> </a:math> . However, the shape of the efficiency curves is also affected by other material properties, such as the energetic disorder, the hopping attempt rate, the relative permittivity, the radiative lifetime, and various other parameters. A sensitivity analysis shows that for materials with <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"> <c:mrow> <c:msub> <c:mi>E</c:mi> <c:mrow> <c:mi>exc</c:mi> <c:mo>,</c:mo> <c:mi mathvariant="normal">b</c:mi> </c:mrow> </c:msub> <c:mo>≈</c:mo> </c:mrow> </c:math> 1.0 eV, the results of FID experiments are nevertheless expected to enable determining <e:math xmlns:e="http://www.w3.org/1998/Math/MathML"> <e:msub> <e:mi>E</e:mi> <e:mrow> <e:mi>exc</e:mi> <e:mo>,</e:mo> <e:mi mathvariant="normal">b</e:mi> </e:mrow> </e:msub> </e:math> with an accuracy of 0.10–0.15 eV. Carrying out FID experiments is therefore expected to become a useful route to quite accurately obtain the electron affinity from the ionization energy, the optical gap, and this measured value of <g:math xmlns:g="http://www.w3.org/1998/Math/MathML"> <g:msub> <g:mi>E</g:mi> <g:mrow> <g:mi>exc</g:mi> <g:mo>,</g:mo> <g:mi mathvariant="normal">b</g:mi> </g:mrow> </g:msub> </g:math> .