Large area growth of MoTe2 films as high performance counter electrodes for dye-sensitized solar cells

Abstract

A cost effective and efficient alternative counter electrode (CE) to replace commercially existing platinum (Pt)-based CEs for dye-sensitized solar cells (DSSCs) is necessary to make DSSCs competitive. Herein, we report the large-area growth of molybdenum telluride (MoTe₂) thin films by sputtering-chemical vapor deposition (CVD) on conductive glass substrates for Pt-free CEs of DSSCs. Cyclic voltammetry (CV), Tafel curve analysis, and electrochemical impedance spectroscopy (EIS) results showed that the as-synthesized MoTe₂ exhibited good electrocatalytic properties and a low charge transfer resistance at the electrolyte-electrode interface. The optimized MoTe₂ CE revealed a high power conversion efficiency of 7.25% under a simulated solar illumination of 100 mW cm^-2 (AM 1.5), which was comparable to the 8.15% observed for a DSSC with a Pt CE. The low cost and good electrocatalytic properties of MoTe₂ thin films make them as an alternative CE for DSSCs.

Figure 1

Schematic illustration of tellurization for the preparation of MoTe₂ from Mo/FTO substrate using a two-zone chemical vapour deposition chamber.

Figure 2

(a–c) Top down FE-SEM images of S1, S2 and S3 (Inset shows the corresponding image of MoTe₂ sample) and (d–f) cross-sectional images of S1, S2 and S3. The observed thickness were ~185 nm, ~335 nm and ~ 668 nm for S1, S2 and S3, respectively.

Figure 3

(a,b) Raman spectra and XRD patterns of MoTe₂ samples.

Figure 4

(a,b) XPS spectra of MoTe₂ samples (a) Mo atoms and (b) Te atoms of S1 and S2, respectively.

Figure 5

(a) CV curves of CEs (scan rate of 20 mVs⁻¹). (b) Nyquist plots of the symmetrical cells; Inset – equivalent circuit and Nyquist plot of symmetrical cell with Pt (R_ct: charge transfer resistance, Z_w: diffusion impedance, R_s: ohmic internal resistance, CPE: constant phase element). (c) Tafel polarization curves of symmetrical cells.

Figure 6

(a) Schematic diagram of the electrocatalytic mechanism in DSSC using MoTe₂ CE. (b) Photocurrent–voltage curves of DSSCs with different CEs, measured at AM1.5 G illumination (100 mW cm⁻²).