Epitaxial lift-off technology produces smooth thin-film solar cells

Flexible thin-film solar cells have long been sought for powering off-the-grid devices where rigid silicon panels are not suitable, and their strong tolerance to radiation and low weight make them an especially good candidate for space applications. As researchers look for thin-film solar cells with higher power conversion efficiency and power density in the labs, difficulties and imperfections in the manufacturing process of these materials have limited their potential for practical applications.

Ding et al. developed an epitaxial lift-off (ELO) technique for fabricating monocrystalline CdTe/MgCdTe double-heterostructure thin-films using water-soluble and nearly-lattice-matched MgTe as a sacrificial layer.

The authors made freestanding CdTe thin-films using hard-baked photoresist as the superstrates with tailored surface tension. According to atomic-force microscopy measurements, the surface of the resulting films was smooth and flat, and the substrates are intact and can be reused to substantially lower the manufacturing cost. The photoluminescence measurements showed that the CdTe thin-films maintain their high optical quality after ELO.

Future devices may benefit from this material, with higher open-circuit voltage and fill factor, which may lead to higher than ever power conversion efficiency for thin-film CdTe solar cells.

“The process can be also used for MgCdTe solar cell with an adequate bandgap to be integrated with silicon cells to form tandem solar cells. One can also use such thin-film material for flexible X-ray detectors and the detector arrays for both medical and industrial X-ray imaging applications,” said author Yong-Hang Zhang.

Source: “Epitaxial lift-off CdTe/MgCdTe double heterostructures for thin-film and flexible solar cells applications,” by Jia Ding, Cheng-Ying Tsai, Zheng Ju, and Yong-Hang Zhang, Applied Physics Letters (2021). The article can be accessed at https://doi.org/10.1063/5.0049377 .