Improved interface passivation in high-efficiency Se-alloyed CdTe solar cells using a SnO <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si17.svg" display="inline" id="d1e400"> <mml:msub> <mml:mrow/> <mml:mrow> <mml:mn>2</mml:mn> </

Thin film cadmium telluride is the most important second-generation solar cell technology. Although the photo-absorber is polycrystalline, high conversion efficiency has been achieved by effectively passivating the grain boundaries and other bulk defects. In this paper, we report on the use of a bilayer SnO 2 /ZnO n-type buffer to improve passivation at the p–n junction interface to achieve 21.7% efficiency. We have assessed the quality of the interface with highly sensitive electrical measurements and a combination of high-resolution electron microscopy and cathodoluminescence. High-resolution cathodoluminescence has enabled the measurement of the recombination velocity to quantify the improvement in interface defect passivation. We have combined this with direct observation of the coherence of the interface at the atomic scale. The use of these techniques will revolutionize our ability to assess future passivation strategies at the front p–n junction and also at the back contact of thin film photovoltaic devices. • A novel n-type bilayer of SnO 2 /ZnO is used to improve passivation of the p–n junction in CdSeTe/CdTe solar cells. • Using the bilayer, a conversion efficiency of 21.7% is achieved for without an anti-reflection coating on the front glass surface. • High resolution transmission electron microscopy (HRTEM) is used to observe the atomic coherence of the p–n junction. • High-resolution cathodoluminescence enables the measurement of the recombination velocity to quantify the improvement in interface defect passivation. • Combining HRTEM with high-resolution CL enables direct assessment of solar cell interface quality.