Measurement of charge carrier mobilities in thin films via the space-charge limited current (SCLC) method; A practical example

Study of space charge limited current (SCLC) transport in charge carrier injection is presented. It is shown that the accurate and convenient calculation of carrier mobility, which has been neglected in many previous studies on transport in optical and electrical devices, is essential to obtain physically meaningful spatial carrier densities and field distributions. In this work, the SCLC technique to accurately determine the mobility of holes and electrons in organic semiconductors is investigated in detail. Recognizing the importance of balanced charge transport to the performance of optical and electronic devices, the fundamentals of SCLC, including Mott-Gurney's law, are discussed and its advantages over alternative methods are highlighted. A carbazole-based compound is used as a practical example, with single-carrier devices fabricated to selectively measure hole-only and electron-only transport. The current-voltage characteristics were analysed in the trap-free SCLC regime (slope ≈ 2 in log-log plots), and yielded mobilities of μ e =4.02 × 10 −5 cm 2 V -1 s -1 and μ h = 1.84 × 10 -3 cm 2 V -1 s -1 . This study not only demonstrates a clear and reproducible method for mobility extraction, but also highlights the importance of SCLC measurements under device-like conditions for material selection and performance optimization in optoelectronic applications.