Kroupa Daniel M, Pach Gregory F, Vörös Márton, Giberti Federico, Chernomordik Boris D, Crisp Ryan W, Nozik Arthur J, Johnson Justin C, Singh Rohan, Klimov Victor I, Galli Giulia, Beard Matthew C
Chemistry & Nanoscience Center , National Renewable Energy Laboratory , Golden , Colorado 80401 , United States.
Department of Chemistry and Biochemistry , University of Colorado , Boulder , Colorado 80309 , United States.
ACS Nano. 2018 Oct 23;12(10):10084-10094. doi: 10.1021/acsnano.8b04850. Epub 2018 Sep 21.
Generating multiple excitons by a single high-energy photon is a promising third-generation solar energy conversion strategy. We demonstrate that multiple exciton generation (MEG) in PbS|CdS Janus-like heteronanostructures is enhanced over that of single-component and core/shell nanocrystal architectures, with an onset close to two times the PbS band gap. We attribute the enhanced MEG to the asymmetric nature of the heteronanostructure that results in an increase in the effective Coulomb interaction that drives MEG and a reduction of the competing hot exciton cooling rate. Slowed cooling occurs through effective trapping of hot-holes by a manifold of valence band interfacial states having both PbS and CdS character, as evidenced by photoluminescence studies and ab initio calculations. Using transient photocurrent spectroscopy, we find that the MEG characteristics of the individual nanostructures are maintained in conductive arrays and demonstrate that these quasi-spherical PbS|CdS nanocrystals can be incorporated as the main absorber layer in functional solid-state solar cell architectures. Finally, based upon our analysis, we provide design rules for the next generation of engineered nanocrystals to further improve the MEG characteristics.
通过单个高能光子产生多个激子是一种很有前景的第三代太阳能转换策略。我们证明，PbS|CdS类Janus异质纳米结构中的多激子产生（MEG）比单组分和核/壳纳米晶体结构的多激子产生有所增强，其起始能量接近PbS带隙的两倍。我们将增强的MEG归因于异质纳米结构的不对称性质，这种性质导致驱动MEG的有效库仑相互作用增加，以及竞争性热激子冷却速率降低。通过具有PbS和CdS特性的价带界面态的多重态对热空穴的有效俘获，冷却过程得以减缓，光致发光研究和从头算计算证明了这一点。使用瞬态光电流光谱，我们发现单个纳米结构的MEG特性在导电阵列中得以保持，并证明这些准球形的PbS|CdS纳米晶体可以作为功能固态太阳能电池结构中的主要吸收层。最后，基于我们的分析，我们为下一代工程纳米晶体提供了设计规则，以进一步改善MEG特性。
