Two-dimensional (2D) materials have attracted attention due to their excellent optoelectronic properties, but their applications are limited by their defects and vacancies. Surface modification is an effective method to restore their performance. Here, ZrSe2 is modified with conductive polymer p-toluenesulfonic acid (PTSA). It is found that PTSA can obtain electrons of ZrSe2 through the combination of −SO3H and ZrSe2, thus forming interfacial dipoles, which improve the work function of ZrSe2. In addition, −OH in PTSA can effectively fill the Se vacancy in ZrSe2 to form P-type doping, thereby improving its conductivity. ZrSe2 modified by the PTSA material is first used as a hole transport layer (HTL) in organic solar cells (OSCs). The efficiency of OSCs based on the PBDB-T:ITIC and PM6:L8-BO binary active layer with ZrSe2:PTSA as the novel HTL reaches 10.66 and 18.14%, which are obviously higher than the efficiency of OSCs with pure ZrSe2 as the HTL (8.48 and 15.64%). More interestingly, the stability of the device with ZrSe2:PTSA as HTL is significantly better than that of PEDOT:PSS. This study shows that the modification of the organic material can effectively improve the photoelectric performance of ZrSe2 and explores the physical mechanism of the interaction between the organic modifier and 2D materials.
Group IVB (Zr and Hf) transition metal dichalcogenides (TMDs) have attracted considerable attention due to their predicted excellent electronic properties that are superior to group VIB TMDs. However, the synthesis of high-quality ZrSe2 layers is seldom reported, greatly hindering the development of this new field. Herein, the epitaxial growth of ZrSe2 on c-plane sapphire substrates is, for the first time, demonstrated using the low-pressure chemical vapor deposition (CVD) method. Impressively, the CVD-grown high-quality ZrSe2 layers exhibit an atomically sharp interface with the underlying substrate, and their epitaxial relationship is determined to be: ZrSe2 (0001)[10–10]||Al2O3 (0001)[11–20]. The electronic band structures of ZrSe2 are calculated using density functional theory methods, showing an indirect band gap of 1.19 eV and a minimum direct band gap of 1.79 eV, respectively. The band gap of ZrSe2 layers is also determined from the UV-visible absorption spectra, which is in good agreement with our band-structure calculations. Furthermore, a photodetector was fabricated based on the CVD-grown ZrSe2 layer on a sapphire substrate, which exhibits a stable and appreciable photoresponse for visible light.
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