Potential of transition metal sulfides, Cu2ZnSnS4 as inorganic absorbing layers in dye-sensitized solar cells

Organic dye sets a benchmark for dye-sensitized solar cell (DSSC) application. Replacing the organic dyes with inorganic phases poses a significant challenge. Without organic dyes, efficiency decreases dramatically due to loss of charge transfer. Thus, surface modification techniques are widely considered to be the key to reducing the electron recombination, suppressing the dark currents and increasing efficiency of DSSC. Using multiple absorbent materials with different energy gaps/band gap values could broaden the DSSC's photon absorption range. This study investigated the potential applications of transition metal sulfides (TMS), kesterite (Cu2ZnSnS4, CZTS) as a promising inorganic absorber layer of DSSCs. Based on the current-voltage measurement, a lower molar ratio of milled CZTS compared to the N719-dye produced a stable DSSC with a power conversion efficiency (η), short-circuit current density (Jsc), and open-circuit voltage (Voc) of 4.75%, 13.99 mA cm−2, and 0.75 V, respectively. Furthermore, incident photon-to-current efficiency (IPCE) analysis exhibited an improved number of incident photons harvested by standard DSSC from 60% to 85% with and without the presence of CZTS. Even when light harvesting reached up to 80%, a higher concentration of CZTS content compared to the N719 dye produced an unstable solar cell device with a low Jsc and η due to electron loss through the recombination process. This was confirmed by the recombination resistance (Rrec) determined by the impedance spectroscopy (EIS), which found that the suppression of the Rrec at a lower ratio concentration between CZTS/N719-dye generated the highest η. The results that the use of the closest concentration of inorganic and organic co-sensitizers can improve the stability and overall performance of the developed DSSC. This approach has been regarded as the most sustainable economically viable means of producing cheap solar cells to convert the largest amount of energy from the solar spectrum to electricity.