Two-Dimensional Nanocrystal Assemblies for Photocapacitive Devices

We describe the emergence of photocapacitance in two-dimensional layered nanocrystal assemblies. Devices are electrically probed by the application of a lateral bias across interdigitated electrodes. We observe capacitive current-voltage characteristics that are individually absent in the nanocrystals. Besides the occurrence of a large zero-bias capacitance, the assemblies further show a transient negative capacitive behavior where the small signal capacitance is found to attain values over a +/- 100 nF range. We show that this system behaves as a damped anharmonic oscillator. Further, the bias dependence of capacitance, characteristics under asymmetric cycling, as well as its relationship with shunt resistance are consistent with the system attaining a transient negative capacitance while migrating around a single energy minimum. We show modulation of the capacitive behavior by incident light enabling the usage of these materials in a photocapacitive detector device.