Colloidal nanoparticles for Intermediate Band solar cells

The Intermediate Band (IB) solar cell concept is a promising idea to transcend the Shockley-Queisser limit. Using the results of first principles calculations, we propose that colloidal nanoparticles (CNPs) are a viable and efficient platform for the implementation of the IB solar cell concept. Focusing on CdSe CNPs, we show that (1) a well-defined intragap state arises inside the gap of the CdSe CNPs, and (2) the intra-gap states of the isolated CNPs with reconstructed surfaces combine to form an IB in arrays of CNPs. This IB is well separated from the valence and conduction band edges. We also show that in solution such IB may be electron doped using, e.g. decamethylcobaltocene, thus activating an IB-induced absorption process. Our results, together with the recent report of a nearly 9% efficient CNP solar cell indicate that colloidal nanoparticle intermediate band solar cells are a promising platform to overcome the Shockley-Queisser limit.