Bipolar charge transport property of N,N′-dicarbazolyl-1,4-dimethene-benzene: A study of the short range order model

Haoyuan Li,Liang Chen,Guifang Dong,Lian Duan,Juan Qiao,Yong Qiu,Liduo Wang

doi:10.1007/s11434-012-5346-1

Abstract

Short range order model is commonly used to explain the charge transport property of disordered organic semiconductors. However, its validity is not yet studied. In this paper, the hole and electron mobilities of a bipolar material, N,N′-dicarbazolyl-1,4-dimethene-benzene (DCB), were measured through time of flight method. The hole and electron mobilities of DCB based on the crystalline structure were calculated. In order to investigate the short range order model, the ratios of charge mobilities at zero electric field of holes to electrons were calculated. The results showed that this model cannot fully explain our case. The reason was discussed in detail, and a correction method was proposed. We showed that using the short range order model without preconditions to explain the charge transport property of amorphous materials may lead to deviations, which is often neglected in the past.

Highlights

Organic amorphous semiconductors were widely applied in devices like organic light emitting diodes (OLEDs), organic thin film transistors (OTFTs) and organic solar cells (OSCs)
Charge mobilities calculations would be performed on the assumption that no external electric field is applied, so that the charge mobilities at zero electric field, (0), must be obtained to compare experimental and theoretical results
Hole and electron mobilities of DCB were calculated based on the crystalline structure. h(0)/ e(0) values of the amorphous film and the crystalline structure were calculated, and the validity of the short range order model was studied

Summary

Introduction

Organic amorphous semiconductors were widely applied in devices like organic light emitting diodes (OLEDs), organic thin film transistors (OTFTs) and organic solar cells (OSCs). One can perform calculations based on the crystalline structure to explain the charge transport properties of amorphous films [4,5,6]. In the short range order model which is used to determine whether a specimen is a hole transporting material or an electron transporting material, one assumes that the ratio of hole zero-field mobility to the electron zero-field mobility in amorphous film is close to that in crystals [2,4,5]. To study the short range order model in our system, the value of the charge mobilities in zero electric field, (0), of holes and electrons were deduced, and the ratios of the (0) of holes to that of electrons were calculated both for calculation and experimental results. The mobility values were calculated from the transit times, , obtained in TOF experiments via the conventional relationship, =d2/ E, where d is the film thickness and E is the applied voltage

Methods

Results

Conclusion