Abstract
Both surface photovoltage and photocurrent enable to assess the effect of visible light illumination on the electrical behavior of a solar cell. We report on photovoltage and photocurrent measurements with nanometer scale resolution performed on the cross section of an epitaxial crystalline silicon solar cell, using respectively Kelvin probe force microscopy and conducting probe atomic force microscopy. Even though two different setups are used, the scans were performed on locations within 100-μm distance in order to compare data from the same area and provide a consistent interpretation. In both measurements, modifications under illumination are observed in accordance with the theory of PIN junctions. Moreover, an unintentional doping during the deposition of the epitaxial silicon intrinsic layer in the solar cell is suggested from the comparison between photovoltage and photocurrent measurements.
Highlights
Since the invention of atomic force microscopy (AFM) at the end of the 1980s [1], various AFM extensions have been developed to perform a wide range of measurements at the nanoscale [2]
Full illumination corresponds to a light intensity of 800 W/m2 which is close to one sun (1000 W/m2) since the open circuit voltage is 460 mV under full light-emitting diode (LED) illumination, comparable to 530 mV measured in a solar cell simulator under one sun
Using the area indented by Conducting probe AFM (CP-AFM) as a geolocalization mark, we could perform measurements within a 100-μm distance, ensuring that the conditions of illumination and the local electrical properties of the solar cell are similar
Summary
Since the invention of atomic force microscopy (AFM) at the end of the 1980s [1], various AFM extensions have been developed to perform a wide range of measurements at the nanoscale [2]. Conducting probe AFM (CP-AFM) and Kelvin probe force microscopy (KPFM) enable, respectively, to sense the local sample current and surface potential and correlate them with the surface morphology Both techniques have gained importance as the new developments in the microelectronic industry often imply nanostructures which require. In contrast with scanning electron and optical microscopy techniques which currently work in the high injection regime, these AFM extensions can perform measurements under real operating injection conditions. They are unique tools to monitor the effect of illumination and electrical bias on solar cell devices at the nanoscale
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