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A correlation between band alignment at an electron transport layer/perovskite interface and the locus of hysteresis in perovskite solar cells is proposed.

Overview of the electronic structure and relevant processes in light absorption and emission for understanding how absorbing and emitting states are connected.

The intricate chemistry occurring at the surface of semiconductor nanocrystals is crucial to tailoring their optical properties to a myriad of applications. This perspective aims to re-evaluate long held ideas in semiconductor nanocrystal surface science in the light of a body of new and rich research. We start by reviewing recent developments in ligand chemistry, followed by a discussion of spectroscopic and computational approaches used for advancing the poorly-understood electronic structure of the surface. With the insights gained, we show how the surface impacts emissive behaviour and we summarize strategies to increase fluorescent quantum yield. This discussion is followed by a review of experimental approaches for quantitative analysis of the surface chemistry at concentrations relevant to spectroscopic measurements. We end by highlighting some new directions in ligand chemistry, namely all-inorganically passivated semiconductor nanocrystals and new applications of surface emission.

We present an introduction to surface-enhanced Raman scattering (SERS) which reviews the basic experimental facts and the essential features of the mechanisms which have been proposed to account for the observations. We then review very recent fundamental developments which include: SERS from single particles and single molecules; SERS from fractal clusters and surfaces; and new insights into the chemical enhancement mechanism of SERS.

The surface-enhanced Raman spectrum of pyromellitic dianhydride (PMDA) on Cu(100) is reported; it is different from that previously reported for the Cu(111) surface. The spectra are sensitive to the incident laser polarization on both surfaces but in different ways. These observations are shown to be inconsistent with a simple classical picture which considers only the interaction of the surface electromagnetic fields with the anisotropic molecular polarizability. They lend additional support to the hypothesis that the chemical enhancement mechanism involves resonance-Raman scattering via a charge-transfer intermediate state. Simulations suggest that the scattering is primarily Franck–Condon and Jahn–Teller in origin.