Poling-Polarization-Mediated Centrosymmetric Charge-Transfer Organic-Cocrystal-Based Flexible Triboelectric Nanogenerator

In the present study, charge transfer (CT) organic cocrystals, with suitable organic donors (D) and acceptors (A), have been synthesized and utilized in the fabrication of a flexible triboelectric nanogenerator (TENG) to harvest mechanical energy. This is based on the principle of triboelectricity. π-donors having excess electron density, namely 1,3,5-tris(4′-aminophenyl)benzene (TAPB) and 3,3′,5,5′-tetramethylbenzidine (TMB) as donor molecules, and π-acceptors, which have reduced electron density, namely 4-nitro-1,8-naphthalic anhydride (NNA), 3,5-dinitrobenzonitrile (DNB), and 1,2,4,5-tetracyanobenzene (TCNB) as acceptors, were utilized in the design of organic cocrystals via CT interactions. A morphological investigation of the synthesized cocrystals was performed through an SEM method. The output performance of the cocrystal-based TENG, namely the output voltage, was measured under the application of a vertical mechanical stress of 0.5 N/cm2, and an observed output voltage in the range of 1.25–2.5 V was obtained. On application of an external dc electric field, the polarization of the charges on the surface of the cocrystal was observed. This behavior surprisingly resulted in a high electrical output voltage (up to 9 V), obtained from the electrically polarized organic cocrystals. Further, modulation in the output voltage was obtained, on increasing the pressure to 50 N/cm2, via human touch, wherein the magnitude of the output voltage increased by 10-fold. The observed output voltages were in the range of 55–62 V and current densities were in the range 0.12–1 μA/cm2, the highest possible magnitude realized so far. A centrosymmetric organic-cocrystal-based device (CC-1) shows a maximum power density of 12.69 μW/cm2 at a load resistance of 4 MΩ. The device generates a durable and stable output current even up to ∼1270 cycles. A real-time application of the TENG as a functional light-emitting diode (LED) has been successfully demonstrated.