Multilayered AgBiP2Se6 has been systematically characterized to be a quasi-direct semiconductor using theoretical calculations and optical experiments. It possesses an indirect bandgap of 1.46 eV and a direct gap of 1.535 eV for simultaneously absorbing the NIR to visible-light photons. In combination with a p-type Ga0.5In0.5Se, a high efficiency p-Ga0.5In0.5Se/n-AgBiP2Se6 stacked solar cell is thus fabricated and demonstrated in this work.
Abstract
AgBiP2Se6 is a ferroelectric semiconductor with a Curie temperature above 300 K which also possesses a variety of functional capabilities. In this work, it is demonstrated that despite its intrinsically indirect bandgap, multilayer (ML) AgBiP2Se6 exhibits unexpectedly strong photoluminescence, attributed to its quasi-direct band structure. The energy difference between the indirect and direct transitions is relatively small (≈0.075 eV), as confirmed by both theoretical calculations and experimental observations. Temperature-dependent optical measurements, corroborated by electronic band structure analysis, reveal the coexistence of indirect (E1ind${mathrm{E}}_{mathrm{1}}^{{mathrm{ind}}}$) and direct (E2d${mathrm{E}}_{mathrm{2}}^{mathrm{d}}$) bandgaps, with phonon-assisted processes playing a significant role in the material’s optoelectronic behaviors. The E1ind${mathrm{E}}_{mathrm{1}}^{{mathrm{ind}}}$ and E2d${mathrm{E}}_{mathrm{2}}^{mathrm{d}}$ transitions at 300 K are determined to be 1.46 and 1.535 eV, respectively. The indirect transition E1ind${mathrm{E}}_{mathrm{1}}^{{mathrm{ind}}}$ is confirmed by transmittance (T) measurement, while the direct transition E2d${mathrm{E}}_{mathrm{2}}^{mathrm{d}}$ is simultaneously detected through micro-photoluminescence (µPL) and micro-thermoreflectance (µTR) measurements. A stacked p-Ga0.5In0.5Se/n-AgBiP2Se6 heterojunction solar cell is successfully fabricated, achieving a photoelectric conversion efficiency (PCE) up to ≈0.583%. Furthermore, AgBiP2Se6 is demonstrated as a promising photocatalyst, exhibiting a high degradation efficiency to organic dyes. ML-AgBiP2Se6 exhibits a quasi-direct bandgap and ferroelectric behavior at room temperature, making it a strong candidate for next-generation electronic, optoelectronic, and environment-protection functions.
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