N-type molybdenum-diselenide-based liquid-junction solar cells: A nonaqueous electrolyte system employing the chlorine/chloride couple

Abstract

Single-crystal, n-type MoSe2 (Eg=1.4 eV) is shown to serve as a stable photoanode in an electrochemical cell employing a nonaqueous (CH3CN) solution of Cl2/Cl- as the redox active material. At 90 mW/cm2 input, 632.8-nm light can be converted to electricity with an efficiency of 5.9-7.5%. The photoanode reaction is 2Cl -→Cl2 and the cathode reaction is Cl 2→2Cl-. The MoSe2 is qualitatively better than MoS2 (∼0.5% efficiency) which has a larger band gap (1.7 eV), but both materials are rugged in the nonaqueous solution, while both photocorrode in aqueous Cl- solutions. In H2O, the I 3-/I- couple is excellent but in CH 3CN it yields lower efficiency than the Cl2/Cl- couple. The stable Cl2/Cl- system provides evidence that a transparent, reversible, non-O2-sensitive redox couple can be useful in n-type semiconductor-based liquid-junction cells employing a direct band gap material having optimum solar response.