The Morphology–Property Effect and Synergetic Catalytic Effect of CdS as Electrocatalysts for Dye-Sensitized Solar Cells

Abstract

In this report, CdS nanoparticle, CdS nanorod, CdS nanorod grown on reduced graphene oxide (CdS nanorod/RGO) and CdS nanoparticle grown on reduced graphene oxide (CdS nanoparticle/RGO) have been synthesized by facile solvothermal method. In order to investigate the morphology-property effect and synergetic catalytic effect of CdS, the electrocatalytic property of four CdS samples are measured as counter electrodes (CEs) of dye-sensitized solar cells (DSSCs). The better catalytic activity and electrical conductivity of CdS nanorod than CdS nanoparticle revealed the morphology-property effect. In addition, CdS/RGO composites exhibited much higher power conversion efficiency (PCE) than pure CdS, demonstrating the synergetic catalytic effect between CdS and RGO. Simultaneously, the PCE value (7.19%) of CdS nanorod/RGO is highest among four CdS samples, which is even comparable to the conventional platinum CE (7.30%). Dye-sensitized solar cells (DSSCs) have attracted tremendous attention in the past two decades, 1,2 due to their high efficiency, lowcost fabrication and environmentally-friendly feature. 3,4 As the crucial component of DSSCs, counter electrode (CE) is in charge of transferring electron and catalyzing the reduction of I 3 − to I − . 5,6 Aiming to reach high performance, CE materials should possess a low sheet resistance, good chemical stability and high catalytic activity toward the CE reduction reaction. 7,8 Platinum (Pt), the conventional CE material, has remarkably high conductivity and efficiently catalyzes the reduction of I 3 − to I − . 9 However, large-scale commercial application of Pt CE in DSSCs is seriously hindered by the high cost and low abundance of Pt. 10,11 In addition, iodine-based electrolyte can easily corrode Pt to PtI 4 and H 2 PtI 6 , worsening the CE performance and raising the cost of DSSC. 12,13 In this regard, it is highly necessary to develop Pt-free and low-cost CE materials with high catalytic activity, electrical conductivity and good chemical stability. 14,15 Among the various CE materials, due to the outstanding charge transfer and catalytic activity, transition metal chalcogenides (TMCs) have presented good electrocatalytic performance for the triiodide reduction and can be a potential material as CEs. [16][17][18] The distinctive electronegativity, valence bond, as well as outer electrons of metal and chalcogens resulted in the specific catalytic activity and electrical conductivity of TMCs. 19 Tang's group has reported that metal selenide alloy CEs highlighted their potential application in robust bifacial DSSCs. [20][21][22] Recently, our previous work has demonstrated the superior catalytic activity, high chemical stability and excellent power conversion efficiency of Bi 2 S 3 , NiSe 2 , Ni 0.85 Se, NiSe-Ni 3 Se 2 , and In 2 S 3 , in addition, we also investigated their morphology-property effect and synergetic catalytic effect in DSSC system. 19,[23][24][25][26][27][28] Cadmium sulfide (CdS), an important TMCs with a bandgap (E g ) of 2.42 eV, has drawn enormous at...

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“…These measured diffraction peaks are highly in agreement with the standard XRD data of JPDS (Card no. 41-1049) for hexagonal wurtzite structures and indicate the formation of CdS films with those structures, as reported in (Mahmood, et al, 2018, Yang, et al, 2018. However, the prominent peaks for the sample CdS pure on the PI substrate marked in Fig.…”

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“…Other diffractions in the XRD pattern are observed at 2θ = 27.05°, 52°, 66°, and 78.88°, attributable to the reflection of CdS at (0 0 2), (1 1 2), (2 0 3), and (2 0 4) which have hexagonal crystal structure, with lattice parameters a = 4.157 Ǻ and c = 6.580 Ǻ (JCPDS card no. 41-1049) [34]. Some small peaks are observed at 2θ = 29.84° and 44.80°, corresponds to the reflection of CdS (2 0 0) and (2 0 0) from the CdS cube (JCPDS card no.…”

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“…The reduction process of I − /I 3 − is facilitated by an electrocatalyst that is located at the CE. 10 Zhang et al 11 described the reactions involved in the reduction mechanism of I 3 − . I 3 − → I 2 (sol) + I − (sol) I 2 (sol) + 2 (surface active site) → 2I (adsorbed) I (adsorbed) + e − → I − …”

“…The reduction process of I − /I 3 − is facilitated by an electrocatalyst that is located at the CE. 10 Zhang et al The CE accelerates the reduction of I 3 − to I − by providing its surface-active sites. The possession of a signicant surface area is crucial for the effective adsorption of mediators in the context of CE.…”