Nanoscale interface mapping of a CdS–CZTS single nanorod heterojunction using Kelvin probe force microscopy

•We have synthesized a single nanorod CdS–CZTS heterojunction which to the best of our knowledge is the first report of its kind.•Kelvin probe force microscopy (KPFM) has been employed to measure and then map distinct regions of surface potential on the nanostructure's surface and this data has been used to correlate junction formation and quality.•When light is incident on the sample there is (a) emergence of a distinct surface potential peak corresponding to the formation of an interface which lies topographically between CdS and CZTS (b) an overall fall in surface potential of the sample by ∼60mV and (c) a relative shift in surface potential between the CdS nanorod and CZTS thin film.•The study analyzes the possible reasons why the charge separation at this interface and consequent extraction is not efficient and this may explain why CZTS has been reported to have device efficiencies which are much lower as compared to CIGS and CIS. In the present study, Kelvin probe force microscopy (KPFM) has been used to study a prototype CdS–CZTS lengthwise single nanorod heterojunction. A shift in surface potential (SP) of the entire sample is observed as the device is taken from dark into light. It has been demonstrated that plots showing the number of pixels with different values of surface potential as a function of the SP itself, can be effectively used to topographically segregate regions composed of different semiconductors. On illumination, a new SP peak emerges and based on its topographical position and SP value, both of which lie in between that of CZTS and CdS, it has been assigned to the heterojunction interfacial layer. These observations have been discussed in terms of junction quality and charge generation and separation to gain a better understanding of the operation of nanorod based solar cell devices.