Spatial Energy Fluctuations Correlated to Fabrication Processes of CdSeTe/CdTe Thin-Films by Confocal Photoluminescence

CdTe-based thin film solar cells have been commercially successful for many years. CdCl<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> treatment and Cu or group-V doping is now ubiquitous in high-performance solar cells. Further device improvement is currently limited by Voc and fill factor. There has been recent discussion about spatial energy fluctuation in CdTe-based solar cells which may be performance-limiting. One technique to probe spatial energy fluctuations is photoluminescence (PL) mapping. However, conventional PL measurements have spatial resolution no smaller than hundreds of microns because of laser spot size and can have artifacts from glass emission. Therefore, a confocal PL technique is implemented to reject glass emission and observe sub-micron spatially resolved PL. To elucidate the origin of energy fluctuations during device fabrication, the confocal PL measurements are carried out layer-by-layer, before and after treatment and doping. It is observed that the CdCl<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> treatment process introduces spatial energy fluctuations and further Cu doping only increases this non-uniformity.