A Solar Cell Architecture for Enhancing Performance While Reducing Absorber Thickness and Back Contact Requirements

A top-surface, micron-scale, protrusion array following unique light management design criteria is presented and demonstrated. Modeling results for absorptance <italic>A</italic>(<italic>λ</italic>) and short-circuit current density <italic>J</italic><sub>sc</sub> along with experimental results for external quantum efficiency and <italic>J </italic><sub>sc</sub> all confirm the advantages achievable for solar cells and photodetectors. While the full modeling utilizes a Maxwell's equation solver, a simplified photon momentum picture is used in the design discussion. As a result of this design 1) less absorber material is required, 2) improved performance over planar top-surface devices is attained with conventional silver (Ag) back reflector/electrodes (BR/Es), 3) importantly employing an Ag-less transparent conductive material on aluminum (Al) BR/E in place of Ag BR/Es leads to even better performance, and 4) counterintuitively performance comparable to cells with Ag BR/Es is attained when a completely metal-less BR/E is employed. The results presented show modeled <italic>J</italic><sub> sc</sub> values of 30.8 mA/cm<sup>2</sup> for a 400 nm nc-Si absorber and measured <italic>J</italic><sub>sc</sub> values of 22.8 mA/cm<sup>2</sup> for 700 nm nc-Si absorber. These results are couched in the context of thin film devices but the design will yield performance enhancement, material savings, and back contact opportunities in any situation where incoming light reaches the BR/E in the corresponding planar control.

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