| Organic semiconductors have gained wide applications in the commercial and industrial sectors due to their advantages such as low cost,processability,and flexibility.A fundamental issue in theoretical research on organic semiconductors revolves around the transport of charge carriers,which plays a crucial role in enhancing the efficiency and performance of organic semiconductor devices and holds paramount importance in the development of novel organic semiconductors.The electronic density of states(DOS),a key parameter determining the electronic and optoelectronic properties of organic materials,exerts an irreplaceable influence on the charge carrier transport processes in organic semiconductors.However,until now,the DOS within disordered organic semiconductors remains incompletely understood.When studying charge carrier transport,researchers primarily rely on speculative DOS functions such as Gaussian DOS,exponential DOS,and their variants.Consequently,this introduces certain inevitable limitations to the related theoretical frameworks for charge carrier transport.Based on the research on the intrinsic nature of DOS function of organic semiconductor,this research undertook a comprehensive examination and exploration of various aspects including the theoretical framework of DOS modeling and its associated parameter theory,the intrinsic mobility of organic semiconductors,the effects of doping on organic semiconductors,and the determination of thermoelectric coefficients in these materials.Drawing upon established classical carrier transport theories,an analytical model was employed to solve the principal equation,enabling simulations to be conducted.The obtained results were subsequently compared with experimental data,and a thorough analysis was performed.The specific research focus of this paper encompasses:Firstly,starting from the most commonly used Gaussian DOS and exponential DOS,and based on the fundamental principle of Poisson flow,we propose a unified DOS,which combining the advantages and characteristics of the two extensively applied models.Subsequently,to achieve a more fundamental understanding of the DOS,we strictly derived a new-type DOS by applying frontier orbit theory and probability statistics.Due to the variety of modified DOS based on Gaussian DOS and exponential DOS and the large number of DOS parameters at the present stage,the physical meaning of DOS parameters is ambiguous and there is a lack of selection criteria.To address this issue,we introduce a general method to establish a quantitative correlation between various DOS parameters and the associated energy disorder.This method facilitates the identification of the physical significance of DOS parameters and offers guidance for their selection.Secondly,we employed classical theories of carrier transport in conjunction with our proposed DOS function model to construct distinct models of organic semiconductor carrier mobility,under both zero(weak)and strong electric field conditions.We further leveraged simulation techniques to analyze and compare our results with experimental data.Some unsolved problems existing in previous literatures are solved,such as organic semiconductor mobility in the full concentration range,organic semiconductor mobility under strong external electric field,mobility saturation under applied electric field,etc.,and the reasons for the limitations of the previous model are explained and analyzed by using our theory.Then,considering current research on organic semiconductor doping model is less than the research on other aspects of carrier transport,we also proposed a new-type doping DOS model and calculated the mobility of dynamic doping in organic semiconductors by using it.The reasons for the limitations of the traditional dopant intrinsic DOS and the influence of each parameter on the dopant DOS model are also analyzed.Finally,by leveraging the DOS model and employing the Miller-Abrahams hopping model along with its variants of escape rate,we constructed two models to computationally determine Seebeck coefficient(thermoelectric coefficient).Utilizing the proposed DOS function model,we conducted comparative analysis between calculated and experimental data in order to assess the thermoelectric coefficient of organic semiconductors.The effects of temperature,concentration,state density and associated parameters on Seebeck coefficient of organic semiconductor were carefully analyzed.Furthermore,by using the previously introduced method to establish the correlation between DOS parameters and energy disorder,we further investigated the influence of energy disorder on Seebeck coefficient with concentration and temperature.This research will enhance our comprehension of the inherent carrier transport mechanism within disordered organic semiconductors,thereby facilitating the improved design of organic electronic devices and the advancement of novel organic device research and development.The findings of this study hold significant research implications and possess substantial application potential. |
