Enhanced multiple exciton generation in PbS|CdS Janus nanocrystals*

Creating multiple excitons from a single high-energy photon is a promising third generation solar energy conversion strategy. Multiple exciton generation (MEG) is particularly efficient in lead chalcogenide nanocrystals (NCs). A recent study showed that heterostructuring nanocrystals, e.g. by making core-shell NCs, can further enhance MEG.[1] However, in core-shell structures, either the photo-generated hole or the electron is difficult to extract.[2] Here, we show that MEG is as efficient in PbS|CdS Janus NCs as in core-shell ones; however, in Janus NCs both electrons and holes can be easily extracted. We also demonstrate that MEG is retained in conductive Janus-particle arrays, with power conversion efficiencies of nearly 3% in proof-of-principle solar cells. Using first-principles simulations we provide insights into the mechanism enhancing MEG in Janus NCs and we propose design rules for next generation nanostructured solar cells.
[1] C. M. Cirloganu et al., Nat. Commun. 5, 4148 (2014).
[2] F. Giberti, M. Vörös, and G. Galli, Nano Lett. 17, 2547 (2017).