Electrical Detection of Singlet Fission in Single Crystal Tetracene Transistors

Abstract

We present the electrical detection of singlet fission in tetracene by using a field-effect transistor (FET). Singlet fission is a photo-induced spin-dependent process, yielding two triplet excitons from the absorption of a single photon. In this study, we engineered a more deterministic platform composed of an organic single crystal FET rather than amorphous or polycrystalline FETs to elucidate spin-dependent processes under magnetic fields. Despite the unipolar operation and relatively high mobility of single crystal tetracene FETs, we were able to manipulate spin dependent processes to detect magnetoconductance (MC) at room temperature by illuminating the FETs and tuning the bias voltage to adjust majority charge carrier density and trap occupancy. In considering the crystalline direction and magnetic field interactions in tetracene, we show the MC response observed in tetracene FETs to be the result of the singlet fission process.

The Effect of Magnetic Fields on Singlet Fission in Organic Semiconductors: its Understanding and Applications

“…[43] The MFEs was also used to confirm the electrical detection of singlet fission which generated photocurrent in an OFET. [23,24] Figure 10 illustrates the photo-induced current as well as magnetoconductance (MC) measurements in a single crystal tetracene FET. As displayed in Figure 10B, the photo-enhanced current was observed in the transistor and the MFEs was investigated to understand the origin of the photo-induced current; As shown in Figure 10C, a large photo-induced MC was detected in the transistor and in the study, the features of singlet fission in MC data was qualitatively explained by a numerical simulation adopting the singlet fission model based on Equation (2).…”

“…As displayed in Figure 10B, the photo-enhanced current was observed in the transistor and the MFEs was investigated to understand the origin of the photo-induced current; As shown in Figure 10C, a large photo-induced MC was detected in the transistor and in the study, the features of singlet fission in MC data was qualitatively explained by a numerical simulation adopting the singlet fission model based on Equation (2). [24] Since it has been shown that an external magnetic field can alter the singlet fission process by its MFEs, it is natural to explore the addition of a permanently existing magnetic field source, such as a ferromagnetic material to the molecular system to find out how it influences the singlet fission process. Figure describes the work on the thin film structure made of two layers, (ferromagnetic) cobalt and tetracene on a glass substrate.…”

“…As we stated earlier, the experimental outcome of the MFEs can originate from both singlet fission and intersystem crossing in a mixed manner if both processes are comparably strong in the system under investigation. [24,45] It was reported that hyperfine interaction and spin-orbit coupling may not change the fundamental mechanism of singlet fission such as the Hamiltonian described in Equation (2). [15,45] However, hyperfine interaction and spin-orbit coupling may induce the intersystem Magneto-photoluminescence for a 10 nm thick tetracene film with and without a 10 nm thick gold layer in place of the cobalt layer.…”

“…[15,17] Since the singlet fission is based on the spin-dependent dynamic processes of the excited states, and thus magnetic fields can influence their behavior, magnetic fields have been used as a powerful tool for studying the properties of singlet fission in organic materials in conjunction with the electrical as well as optical techniques. [18][19][20][21][22][23][24] Hence, understanding the MFEs in singlet fission can play a pivotal role in developing and advancing singlet fission-based molecular systems. [15,[18][19][20][21][22][23][24] This review first describes the basics of the MFEs involved with the intersystem crossing between a singlet and a triplet excited state of molecule-based systems due to intrinsic interactions such as spin-orbit coupling and hyperfine interaction, and then it extends to the discussion of the MFEs on singlet fission (and triplet fusion) by summarizing the experimental as well as theoretical studies.…”

“…[18][19][20][21][22][23][24] Hence, understanding the MFEs in singlet fission can play a pivotal role in developing and advancing singlet fission-based molecular systems. [15,[18][19][20][21][22][23][24] This review first describes the basics of the MFEs involved with the intersystem crossing between a singlet and a triplet excited state of molecule-based systems due to intrinsic interactions such as spin-orbit coupling and hyperfine interaction, and then it extends to the discussion of the MFEs on singlet fission (and triplet fusion) by summarizing the experimental as well as theoretical studies. Since both the intersystem crossing and the singlet fission may coexist in organic molecules, it is advised to be aware of the MFEs on both phenomena for understanding experimental results correctly.…”