Hot Carrier Solar Cells in the Dark

Electro-luminescence and dark I-V are important characterisation tools for photovoltaic devices. Optoelectronic reciprocity between emission of light due to an externally applied bias and the generation of current due to the absorption of light means that the external quantum efficiency of the device is imprinted onto the electroluminescent emission, while the dark I-V gives valuable information on the recombination and resistive properties of the device. One of the fundamental assumptions in the usual optoelectronic reciprocity relation is that the temperature of the carriers is always equal to the temperature of the lattice in the device. When designing a hot carrier solar cell (HCSC) the aim is to break this assumption and maintain the carriers in the absorber at a temperature larger than the temperature of the carriers in the contacts and, consequently, the temperature of the lattice. To exploit this temperature difference for power generation, an electronic heat engine is required, which is usually envisaged as an energy selective contact or an energetic barrier to carrier extraction.<br/>In this contribution we explore how the combination of slow electron cooling and energy selective contacting should manifest itself in the dark [1]. We investigate ideal energy selective contacts as well as thermionic barriers in both - the impact ionization and the carrier conservation - model of hot carrier solar cells. This theoretical exploration paves the way for a novel, yet simple, characterisation method that complements photoluminescence and time-resolved techniques to understand hot carrier properties. Examining the device in the dark allows for the characterisation of the properties of both, the absorber material itself and the contact architecture.<br/>[1] A. Pusch et al. “Optoelectronic reciprocity in hot carrier solar cells with ideal energy selective contacts”, Progress in Photovoltaics <b>29</b>, 433-444 (2021)