Abstract
Quantum coupling in arrayed nanostructures may induce novel mesoscale properties such as electronic minibands that may lead to applications including high efficiency solar cells. Colloidal PbSe quantum dots (QDs) can self-assemble into epitaxially-fused superlattices (epi-SLs), making them a promising material system to study collective phenomena. In the present study, the presence of distinct local electronic states induced by crystalline necks connecting individual PbSe QDs is documented by several techniques that leads to modulation of the band gap energy across the epi-SL. The energy band gap measured by multi-probe scanning tunneling spectroscopy (STS) shows variation from 0.7 eV at the center of the QDs to 1.1 eV at their necks. Complementary monochromated electron energy-loss spectroscopy (EELS) measurements reveal the presence of distinct electronic states from necks in the epi-SL, confirming the STS measurements and demonstrating band gap modulation in spectral mapping. It is hypothesized that these new electronic states are induced by quantum confinement of carriers in the necks between the QDs, redefining the energy landscape of the PbSe QD epi-SL.
Defect passivation of perovskites in high efficiency solar cells
