Understanding where the photovoltage is generated in a solar cell and where energy losses occur is a key aspect for the development of any solar cell technology. In time-resolved photoelectron spectroscopy, photo-induced core level shifts can be measured as a function of pump-probe delay time and used to determine how the electric field between sample surface and substrate changes upon illumination. This gives insight how the photovoltage in the cell rises and decays over time. We have previously used this technique at a synchrotron to follow the charge separation and recombination between a lead sulphide quantum dot layer and an electron transport layer from pico- to microsecond timescales.¹

In this talk, I will examine different cases where the photovoltage is either generated between the sample surface and bulk or at a buried interface and show how the investigated photovoltage depends on sample design. I will then present how we have extended our previous study to investigating the photovoltage generation in different parts of the quantum solar cell through sample design. In addition to investigating charge separation to an electron transport layer, we also investigated the photovoltage generation at the junction between p- and n-type quantum dot layers. The results are then compared to the photovoltage generation in a full quantum dot solar cell, where a gold contact is present. The highest photovoltage was generated in this latter case, and the presence of the gold contact also led to a decrease in the charge recombination rate.

Finally, I will discuss how this technique could be applied to other solar cell technologies and what potential the technique has for giving insights into the development of solar cells.

1 T. Sloboda et al., A method for studying pico to microsecond time-resolved core-level spectroscopy used to investigate electron dynamics in quantum dots, Sci. Rep., 2020, 10, 22438.