The hot carrier solar cell is a heat engine; supplementing or supplanting the photovoltaic action of a traditional solar cell with a thermally driven current, analogous to a thermoelectric device. With this additional channel for energy extraction it is, in principle, possible for these cells to achieve efficiencies up to 85%, since the thermalization loss of high energy carriers is mitigated through their contribution to the heat current. In this thesis, three different hot carrier solar cell concepts are presented and experimentally investigated to probe their efficacy.
Firstly, a hot carrier solar cell structure is presented, in which photogenerated carriers are extracted from a narrow band gap semiconductor to a wider bandgap semiconductor through a double barrier quantum well, providing energy selective extraction through resonant tunnelling. Current-voltage characteristics of this cell are presented along with time-resolved and temperature-dependent photoluminescence data, supporting the conclusion that this cell is operating as a hot carrier cell.
Secondly, the idea of a metallic absorber for a solar cell is proposed, in order to provide ultra-high absorption of light (>99%) in metallic films thinner than 10nm. This idea is realised in two different cells, with silver and chromium absorbers. The absorption of light in the metal film, followed by extraction of heated electrons over a Schottky barrier, is demonstrated.
Thirdly, the combination of these ideas is discussed, and a solar cell with a metallic absorber and selective extraction of heated electrons through resonant tunneling is realised. The current-voltage characteristics of all cells are modelled theoretically, and key signatures are revealed in both experimental and theoretical work showing the extraction of heated carriers.Open Acces
