Study On The Fabrication And Performance Of Photovoltaic Device Based Polyoxometalates And ZnO

Solar energy, as the cleanest and least limited energy source, is seriously considered asan alternative to the conventional fossil fuels. ZnO is a promising, wide band gapsemiconductor oxide. The conduction band edge of both ZnO and TiO2is located atapproximately the same level while the electron mobility in ZnO is much higher. It iswell-known that high mobility of the excited electrons is more favorable for the collection ofphotoinduced electrons. The enhancement of photovoltaic response is still desired forrealizing effective utilization of ZnO films. An intelligent strategy is to incorporate anelectron accepting medium into the ZnO film to effectively retard the photo-excitedelectron–hole recombination and to tailor the charge transport properties.Polyoxometalates (POMs) are a good kind of electron acceptor and have the ability topromote the electron transfer rate of the semiconductor conduction band (CB) by trappingphotogenerated electrons. POMs are also a possibility be used as the electron acceptors totransfer electrons from the CB of ZnO to an inert electrode, which promotes the overalllight-to-electricity conversion efficiency. Such a donor–acceptor structurecould retardeffectively the fast charge pair recombination so as to enhance the photovoltaic response ofZnO. we fabricated a photosensitized electrode consisting of POMs (SiW12) and ZnO by anelectrochemical deposition method. The electrochemical deposition allows precise control ofthe morphology and, more importantly, good electrical contact between SiW12–ZnO andconductive substrates. By using the SiW12–ZnO composite film as photoanodes for the solarcell, an overall power conversion efficiency of0.79%was obtained.To further explore the effects of polyoxometalate on the photovoltaic properties of ZnO,we prepared the ZnO/TiO2film, the ZnO/SiW12/TiO2film, the ZnO/N719film and theZnO/SiW12/N719film by electrodeposition and doctor-blade methods, and then the filmswere characterized in terms of morphology. The photovoltaic properties were investigated byassembling the DSSC device based on these hybrid films. The results of current-voltagemeasurements indicated that the introduction of POMs markedly enhanced photovoltaicperformance of ZnO/TiO2cells. Especially, the ZnO/N719hybrid film displayed a one-foldimprovement in energy conversion efficiency, from0.47%to0.97%. The above results furtherdemonstrate the POMs are a good kind of electron acceptor and have the ability to promotephotogenerated electron transfer rate, which has great potential value in improving the energyconversion efficiency of the photovoltaic cells.Phthalocyanine molecules should be of good candidates because they are not only organic semiconductor but also sensitizers having high absorption coefficients, reasonablechemical stability and good compatibility with ZnO. Thus, the electrodeposition of ZnO in thepresence of phthalocyanine (Pc) or its derivatives has been proposed as an innovativeapproach to prepare photoanode hybrid materials for DSSC. We explore the one-stepelectrodeposition of ZnO with tetrasulfonated copper phthalocyanine (CuTSPc) by aconstant-current mode. The films ZnO/CuTSPc was characterized in terms of morphology andcrystallinity, and the photovoltaic properties were also investigated by assembling the DSSCdevice based on the ZnO/CuTSPc hybrid films. Photoelectrochemical measurements indicatedthat the CuTSPc plays a significant role in enhancing photoelectrical performance. TheCuTSPc could increase the absorption of the incident photons, which leads to rapid chargetransfer and effective interface recombination restriction. Thus, the DSSC based onZnO/CuTSPc shows a three-fold improvement in energy conversion efficiency than that theonly ZnO-based DSSC.