Determining the quality of photosupercapacitors and photobatteries in different modes of operation - A new approach

Monolithically integrated photosupercapacitors and photobatteries (photostorage devices) are a growing field of research and development. Yet there is currently no universally agreed-upon figure of merit for these devices that is independent of arbitrary testing parameters and also applicable to all possible operating scenarios. In this work we address this issue by introducing a way of defining a set of quality functions that can be evaluated unambiguously for any given device and that provide useful metrics for all operating scenarios. This is achieved by first identifying three distinct fundamental modes of operation for a photostorage device. Secondly we demonstrate a method to calculate a quality function for each mode from the parameters of an equivalent circuit model. This strategy avoids using variable physical parameters to evaluate a real device, such as a capacitance that depends on an arbitrary charging or discharging current. Rather, the combination of the three fundamental modes of operation and the constant nature of the model parameters allows a rigid definition of the quality of a device and reliable predictions of its performance under any conditions. This could serve to better compare the performance of photostorage devices and to determine design criteria in view of specific applications.