Zeolitic-imidazolate frameworks derived Pt-free counter electrodes for high-performance quantum dot-sensitized solar cells

Zeolitic-imidazole frameworks (ZIFs), as novel porous materials, are attracting much attention in several fields due to their special advantages such as large specific surface area, versatile porosity and well-connected networks. Here, we develop a porous ZIF-derived catalytic thin film, which was coated on the conducting glass as a counter electrode (CE) to substitute costly platinum for quantum dot-sensitized solar cells (QDSSCs). A ZIF layer is first prepared by coating ZIF-67 powders on the conducting glass, followed by the careful calcination treatments in sulfur vapour (sulfuration) or nitrogen gas (carbonization). The structure and morphologies of the derived porous film are characterized by the measurements of XRD, SEM and BET, and the electrochemical properties in the polysulfide solution are evaluated by the measurements of Tafel curves and electrochemical impedance spectroscopies. The derived porous film is used as a CE to fabricate QDSSC with CdSe quantum dot-sensitized TiO2 nanocrystalline thin film and the polysulfide solution. Compared with the photovoltaic performance of CdSe QDSSCs based on the CE prepared by the different sulfuration conditions, QDSSC based on the CE derived by the sulfuration for 30 min shows an excellent light-to-electric conversion efficiency of 3.77%, it is even higher than that of QDSSC based on Pt CE (2.98%). This work will open a new avenue to design a facile, low-cost and renewable CE for QDSSC.