Simple Chemical Synthesis Of Niobium-based Compounds And Their Applications To DSSCs

Dye sensitized solar cells?DSSCs?,a new generation of photovoltaic technology,have attracted significant attention due to their low production cost,easy manufacture,high power conversion efficiency?PCE?,and environmental-friendliness.Being a key part of DSSCs,counter electrode?CE?mainly collect electrons from the external circuit and catalytically reduce the I3-ions in the electrolyte.The noble metal Pt is the conventional CE material in DSSCs.However,Pt is scarce in the nature,high cost,and corroded easily by the I-/I3-electrolyte,which greatly hinder the commercial application of DSSCs.Because transition metal compounds?TMCs?have similar electronic structures as Pt,they have been identified as ideal substitutes for Pt CE materials.Furthermore,TMCs are becoming more popular among researchers for producing CEs due to the high abundance of raw material,the wide variety of production techniques,and some other excellent catalytic activity.This study synthesized and evaluated the electrochemical properties of three types of oxidized niobium including Nb₂O₅,Nb₂O₅@NbO₂,and NbO₂.The results show that the three types of oxidized niobium CEs not only have excellent catalytic activities,they also possess high electrochemical stability.Among the three,the Nb₂O₅@NbO₂ produced in 800? has the smaller charge-transfer resistance?Rct??7.74?·cm-2?.The corresponding DSSCs also have good photovoltaic parameters: a short-circuit current?Jsc?of 12.85mA·cm-2,an open-circuit potential?Voc?of 0.72 V,a fill factor?FF?of 0.55,and a PCE of 5.03%.The NbO₂ is heated with the nitriding process to study the effects of nitriding temperature on the chemical composition of the product.Results showed that NbO₂ was efficiently transformed into Nb3.49N4.56O0.44?700??or NbN?900??by modifying the nitridation temperature.Results of electrochemical properties show that the ternary compound,Nb3.49N4.56O0.44,has better catalytic activity and electrochemical stability than NbO₂ and Nb N,with an Rct of 4.47?·cm-2.With the same ternary compound applied to DSSCs,the CE have Jsc?16.06mA·cm-2?higher than that of Pt?15.77mA·cm-2?,Voc equal that of Pt?0.70V?,and comparable FF and PCE?0.57 vs.0.65,6.36% vs.7.19%?.In addition,we prepared the niobium-based compound,Fe?NbO3?2,by the ‘two-step' method,and studied its electrochemical and photovoltaic properties.The results show that Fe?NbO3?2 CEs have catalytic activity and electrochemical stability comparable to that of Pt CEs,with an Rct of 7.95?·cm-2.Applying the Fe?Nb O3?2 CE to DSSCs,we obtain the following photovoltaic parameters: a Jsc of 15.38 m A·cm-2,a Voc of 0.74 V,an FF of 0.50,and a PCE of 5.65%.Under the same conditions,Pt CEs have a Jsc of 13.78mA·cm-2,a Voc of 0.72 V,an FF of 0.67,and a PCE of 6.71%.