Multidentate anchoring through additive engineering for highly efficient Sb₂S₃ planar thin film solar cells

Sb₂S₃ is a promising candidate for the flexible solar cells or the top subcells in tandem solar cells due to its wide-bandgap, less toxic, acceptable cost and progressive power conversion efficiency (PCE). However, the poor quality and high trap states of Sb₂S₃ films limit the device performance further enhancement. Herein, we adopt a multidentate ionic liquid, tetramethylammonium hexafluorophosphate ([TMA][PF₆]) as a novel additive to address this issue. The octahedral [PF₆]⁻ contains six different oriented fluorine atoms with the lone pair electrons, which could coordinate with Sb atoms due to the multidentate anchoring. Thus, the high-quality Sb₂S₃ film with low trap states has been achieved. Moreover, the Fermi level of the Sb₂S₃ film has been upshifted, thereby showing an effective charge transfer. As a result, all photovoltaic parameters of the optimized Sb₂S₃ devices are obviously enhanced, boosting the final PCE from 4.43 (control device) to 6.83 %. Our study about the multidentate anchoring is manifested to be an effective method to enhance the Sb₂S₃ device performance.