Contents lists available at ScienceDirect Solar Energy Materials & Solar Cells journal homepage: www.elsevier.com/locate/solmat Surface potential investigation on interdigitated back contact solar cells by Scanning Electron Microscopy and Kelvin Probe Force Microscopy: Effect of electrical bias Paul Narchi a,b, ⁎ , Vladimir Neplokh c , Valerio Piazza c , Twan Bearda d , Fabien Bayle c , Martin Foldyna b , Chiara Toccafondi b , Patricia Prod’homme a , Maria Tchernycheva c , Pere Roca i Cabarrocas b a TOTAL New Energies, 24 cours Michelet, 92069 Paris La Défense Cedex, France b LPICM, CNRS, Ecole Polytechnique, Université Paris-Saclay, 91128 Palaiseau, France c Institut d’Electronique Fondamentale, UMR 8622 CNRS, University Paris Sud, University Paris Saclay, 91405 Orsay, France d IMEC, Kapeldreef 75, B-3001 Leuven, Belgium ARTICLE INFO Keywords: Interdigitated back contact Heterojunction Solar cells Silicon Kelvin Probe Force Microscopy Scanning Electron Microscopy ABSTRACT Both Kelvin Probe Force Microscopy and Scanning Electron Microscopy enable assessment of the effect of electrical bias on the surface potential of the layers of a solar cell. We report on a comprehensive comparison of surface potential measurements on an interdigitated back contact solar cell using these two techniques. Measurements under different values of electrical biases are performed on and between the metallic contacts. They show a good agreement between the surface potential obtained with Kelvin Probe Force Microscopy and the Scanning Electron Microscopy signal. In order to provide an accurate comparison, the scanned areas are adjacent to each other and accurate repositioning is achieved thanks to a nano-indentation between the contacts. We show that measurements under reverse bias are of interest to locate nano-defects and measurements under forward bias are relevant to identify local series resistance issues. We suggest that a setup combining Scanning Electron Microscopy and Kelvin Probe Force Microscopy under different values of the electrical bias should be valuable since the former is a high throughput technique enabling measurements on large scan areas, while the latter is a quantitative, low noise, and unintrusive local technique. 1. Introduction Interdigitated back contact (IBC) solar cells are a promising design to reach high conversion efficiencies. In this architecture, both p and n contacts are positioned on the rear side of the cell with the shape of two interdigitated combs. This design avoids reflection losses on the front side of the cell, contrary to the case of traditional solar cells. The latest crystalline silicon solar cells showing the record efficiencies belong to IBC family. For instance, Sunpower has recently presented 25% efficient industrially feasible solar cells [1] and Kaneka has announced a 26.33% laboratory world record [2] using this design. In order to approach the theoretical limit of 29% efficiency for crystalline silicon solar cells [3] remaining losses have to be reduced. Among them, electrical losses mainly come from local series resistance due to poor local contacts and long current paths [4]. In this perspective, the investigation of series resistance and electrical defects at the nanoscale becomes of interest to localize the areas of power losses in IBC solar cells. Local series resistances cause surface potential drops that can be monitored with several characterization techniques. In this work, we focus on two of them: Kelvin Probe Force Microscopy (KPFM) and Scanning Electron Microscopy (SEM). KPFM is a scanning probe microscopy technique that measures the surface potential of a sample by monitoring the amplitude of the AFM cantilever operated in tapping mode. KPFM has proven to be an effective tool to investigate the electrical behavior of solar cells at the nanoscale. For instance, measurements on the cross-section of solar cells have enabled monitoring the effect of illumination [5] and electrical bias [6] on the PN junction properties of solar cells. SEM is an electron microscopy technique that is routinely used to study the surface topography of materials at the nanoscale. However, it http://dx.doi.org/10.1016/j.solmat.2016.12.009 Received 21 June 2016; Received in revised form 14 October 2016; Accepted 2 December 2016 ⁎ Corresponding author at: TOTAL New Energies, 24 cours Michelet, 92069 Paris La Défense Cedex, France. E-mail address: paul.narchi@polytechnique.edu (P. Narchi). Abbreviations: AFM, Atomic Force Microscopy; a-Si, H: hydrogenated amorphous silicon; IBC, Interdigitated Back Contact Solar Cell; ITO, Indium Tin Oxide; J(V), current density – voltage; KPFM, Kelvin Probe Force Microscopy; SE, Secondary Electrons; SEM, Scanning Electron Microscopy Solar Energy Materials & Solar Cells 161 (2017) 263–269 0927-0248/ © 2016 Elsevier B.V. All rights reserved. MARK