Analysis of solar cell quality using voltage metrics

The highest efficiency solar cells provide both excellent voltage and current. Of these, the open-circuit voltage (V_oc) is more frequently viewed as an indicator of the material quality. However, since the V_oc also depends on the band gap of the material, the difference between the band gap and the V_oc is a better metric for comparing material quality of unlike materials. To take this one step further, since V_oc also depends on the shape of the absorption edge, we propose to use the ultimate metric: the difference between the measured V_oc and the V_oc calculated from the external quantum efficiency using a detailed balance approach. This metric is less sensitive to changes in cell design and definition of band gap. The paper defines how to implement this metric and demonstrates how it can be useful in tracking improvements in V_oc, especially as V_oc approaches its theoretical maximum.