Theoretical study of the strong piezo-phototronic effect in 2D monochalcogenides for multi-junction solar cells

The piezophototronic effect is a new scientific area that investigates the synergistic interactions of piezoelectric, semiconductor, and photoexcitation features. This effect is seen in crystals lacking inversion symmetry, where applied strain alters electronic transport and provides a way to modify material properties. Monolayer 2D semiconductors, such as transition metal dichalcogenides (TMDCs) and group IV monochalcogenides, have higher piezoelectric coefficients than conventional piezoelectric materials. This study proposes the development of a stable, high-performance multijunction solar cell (MJSC) leveraging the piezo-phototronic effect. The emphasis is on single-type 5-layer 2D monochalcogenides (SnS, SnSe, GeS, and GeSe) with the assistance of strain engineering. Surprisingly, the ultrathin parallel-connected solar cell achieves an electric power conversion efficiency of over 31% when tested under blackbody radiation, surpassing the recognized Shockley–Queisser (S-Q) limit. The piezophototronic effect improves solar cell performance while also addressing voltage mismatch issues. This work introduces a novel approach to developing and manufacturing high-efficiency and robust monolayer multijunction photovoltaic solar cells (MJPSC) based on 2D monochalcogenides.