A consolidated account of electrochemical determination of band structure parameters in II-VI semiconductor quantum dots: a tutorial review

Probing absolute electronic energy levels in semiconductor quantum dots (Q-dots) is crucial for engineering their electronic band structure and hence for precise design of composite nano-structure based devices. The use of electrochemistry has allowed us to investigate size, shape and composition dependent band structure parameters viz. the conduction band edge, valence band edge & quasi-particle gap and to establish novel charge induced phenomena in colloidal semiconductor Q-dots. The electrochemical behavior is also of special importance for the prediction of the stability of Q-dots in biological environments as well as for precise design of composite nanohetero-structures for opto-electronic (light emitting diodes) and photovoltaic (solar cells) applications. Several researchers have contributed to probing and predicting the positions of absolute energy levels of band edges and surface states as well as to the establishment of a potential window of stability for a wide variety of Q-dots both in aqueous media and in organic solution. The crucial point about these studies is that unlike spectroscopic methods, no unified approach has been followed and a variety of methods and protocols have been developed to carry out these measurements either on diffusing or thin films of Q-dots in different electrolyte media viz. aqueous, organic and ionic liquids, each having their own advantages over the others. However, a consolidated account of these methods and protocols is not available in the literature. The aim of this tutorial review is therefore to consolidate and compare the studies related to the determination of the band structure of II-VI semiconductor Q-dots through electrochemical measurements. A brief introduction to electrochemical techniques, especially cyclic voltammetry, is given, followed by a summary of experimental methods developed for these measurements. Finally, a concise protocol that can be easily applied universally and is attractive for other users dealing with semiconductor Q-dot based devices is discussed.