CdTe Solar Cells at the Threshold to 20% Efficiency

After a long period of stagnancy for record cell efficiency and several years of growth of the industry, CdTe solar cell efficiency has been rapidly increasing recently. First Solar (FSLR) fabricated an 18.7% NREL certified cell at the end of 2012 and reports an increase to a certified 19.0% in this paper. Although the improvements were dominated by increases in short-circuit current and fill factor, there is now evidence that the open-circuit voltage of polycrystalline CdTe is not fundamentally limited to ~850 mV, and first devices exceeding 900 mV have been demonstrated. In-depth device characterization indicates that the responsible third-level metric is the increase of carrier lifetime, which can be characterized by transient photoluminescence. The progress at hand suggests that the near-term achievable target for CdTe solar cells should be raised from 19% to 22%. A detailed numerical model is used to translate cell results into predicted module efficiency. These simulations are in agreement with FSLR´s recently certified 16.1% total-area module efficiency record. Forward-looking simulations show that with already demonstrated technology components, a module efficiency exceeding 17% is attainable. Disruptive changes and implementation of new device architectures can provide further room for improvement for cell efficiency beyond 22%.