Effect of rapid thermal annealing on the Mo back contact properties for Cu2ZnSnSe4 solar cells

•An RTP annealing applied for the first time on Mo for CZTSe solar cells.•Clear improvement of the efficiency from 5.7 to 7.6% with RTP treatment.•Discussion of this improvement with adequate material/device characterizations.•Stress-induced defects responsible of the electrical leakage are revealed.

The effect of a rapid thermal process (RTP) on the molybdenum (Mo) back contact for Cu2ZnSnSe4 (CZTSe) solar cells is here investigated. It is shown that the annealing of the Mo layer during 5 min at 550 °C, not only improves the crystalline quality of the back contact (avoiding the absorber decomposition at this region because Mo becomes more resistant to the selenization), but also helps achieving higher crystalline quality of the absorber with bigger grains, reducing the current leakage through the heterojunction. We demonstrate that this is related to the relaxation of the compressive stress of the CZTSe absorber, when synthesized on the RTP annealed substrates. CZTSe solar cells prepared on annealed Mo films exhibited higher short circuit current densities and higher open circuit voltages, resulting in 10% and 33% higher fill factors and efficiencies.

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