Investigation of magneto-photoluminescence and magneto-photocurrent in rubrene-based blending devices

Abstract

In order to investigate the microscopic evolution process of different types of excitons in rubrene blending systems, this study fabricated a series of organic optoelectronic devices consisting of 5,6,11,12-tetraphenylnaphthacene (rubrene) blended with Tris(2,4,6-triMethyl-3-(pyridin-3-yl)phenyl)borane (3TPYMB). It then systematically measured the photoluminescence and photocurrent magnetic field responses of the devices with different blending proportions at different temperatures and applied voltages. The study found that the temperature-dependent magneto-photoluminescence (MPL) curves of the blending devices presented a W-like line-shape under zero bias voltage, while the magneto-photocurrent (MPC) curves showed an unreported M-like line-shape. The temperature dependences of high field effect and low field effect for the MPC curves demonstrated different evolution regulations. At the same time, the amplitudes of MPC curves changed from positive to negative signs with positive bias current. By analyzing these interesting variations in the curve line-shapes, we found that the W-like line-shape curves are caused by a magnetic-field-mediated singlet fission (STT) process. The rise in the MPC curve at low magnetic field can be attributed to the effect of the intersystem crossing (ISC) process, and the fall in the MPC curve at high magnetic field is caused by the triplet-charge annihilation (TQA) process. The positive to negative change in MPC amplitude is related to the intensity of electric injection carriers. This work not only contributes to the understanding of the microscopic mechanism of photoluminescence and photocurrent in organic optoelectronic devices, it can also serve as a reference for further optimizing the performance of rubrene-based optoelectronic diodes in the future.