Annealing (glass)

Epitaxy

Metallurgy

Materials science

Layer (electronics)

Nanotechnology

CZTS

Solar cell

Heterojunction

Energy conversion efficiency

Kesterite

Optoelectronics

Nature Energy

The conversion efficiency of kesterite solar cells has been stagnated at 12.6% since 2013. In contrast to chalcopyrite solar cells, the performance of kesterite solar cells is seriously limited by heterojunction interface recombination. Here we demonstrate kesterite/CdS heterojunction is constructed on a Zn-poor surface due to the dissolution of Zn2+ during chemical bath deposition. The occupation of Cd2+ on the Zn site and re-deposition of Zn2+ into CdS creates a defective and lattice-mismatched interface. Low-temperature annealing of the kesterite/CdS junction drives migration of Cd2+ from absorber back to CdS and Zn2+ from absorber bulk to surface, achieving a gradient composition and reconstructing an epitaxial interface. This greatly reduces interface recombination and improves device open-circuit voltage and fill factor. We achieve certified 12.96% efficiency small-area (0.11 cm2) and certified 11.7% efficiency large-area (1.1 cm2) kesterite devices. The findings are expected to advance the development of kesterite solar cells. The efficiency of kesterite solar cells has been stuck at 12.6% since 2013 due to challenges in controlling defects. Now Gong et al. present a low-temperature annealing of the kesterite/CdS junction to form an epitaxial interface with a low defect density, enabling 13%-efficiency devices.

Elemental de-mixing-induced epitaxial kesterite/CdS interface enabling 13%-efficiency kesterite solar cells