The Study Of The Application Of Polyoxometalate-TiO₂Composite Film In Photovoltaic Devices And Electrochromic Devices

Exploring new energy and energy saving both play important roles in attaining thepurpose of sustainable development. Dye sensitized solar cells （DSSCs） are promisingphotovoltaic device in the utilizing of solar energy. Electrochromic （EC） smart windows maybe electronically darkened or lightened with small applied voltages, allowing for controllingof daylight, solar heat gain, and internal heat loss through windows of the buildings andvehicles. Polyoxometalates （POMs） represent a well–known class of metal oxide nanoclusterswith intriguing structures and electrochemical properties, which have extreme potential to beapplied in photovoltaic and electrochromic devices. In this paper, POMs–TiO₂compositefilms have been fabricated by layer–by–layer （LBL）, screen printing method andelectrodeposition method. The POMs–TiO₂composite films are successfully applied inDSSCs and EC smart windows. The performances of the devices have been fully tested.1. A new H3PW₁₂O40(PW₁₂)–based interfacial layer for DSSCs has been fabricated by LBLmethod. The cells have been systemically tested by photocurrent–voltage curve,dark–current measurement, open–circuit voltage decay and the monochromatic incidentphoton–to–photocurrent conversion efficiency techniques. The PW₁₂–based interfaciallayer accelerates electron transfer and retards recombination, eventually leading to theenergy conversion efficiency increase efficiently. The investigations indicate that theenergy conversion efficiency of (PW₁₂/TiO₂)3–DSSC is significantly enhanced by54%at100mW cm–2compared with the DSSC with no–treatment and20%compared withTiCl4–treatment DSSC. POM is firstly introduced to the interfacial layer in modifying thephotoanode to accelerate electron transfer and retard recombination for improving theefficiency of DSSC in this work.2. PW₁₂–TiO₂composite have been successfully introduced into the photoanode of thedye–sensitized solar cells to reduce the recombination of the electrons which results inlonger electron lifetime. The cells with PW₁₂modified photoanodes show betterperformance than the cell with pure P25photoanode. The overall improvement of theefficiency is22.8%by using the PW₁₂modified photoanode. The effect of the POM wasstudied by electrochemical impedance spectroscopy and open–circuit voltage decaymeasurement. The results show that the electron lifetime becomes longer following by theincreasing of the amount of the PW₁₂.3. A new electrodeposited method has been explored to prepare POMs-porous TiO₂composie films. The composite films have been applied in EC smart windows. It is a simple and low cost process to prepare the EC film by the solution–basedelectrodeposition method. The [NaX5W30O110]n–（X=P, n=14; S, n=9）–based EC smartwindows perform high transparency in bleach state, high optical contrast, long durability,and high coloration efficiency.4. Using the electrodeposite method the performance of the The Wells–Dawson type POMK6[P2W18O62]14H2O （P2W18） and its derivate K10[P2W17O61]20H2O （P2W17） has beenelectrodeposited on porous TiO₂substrate and applied in EC smart windows. Themaximum optical contrast for the P2W17–based EC smart window is93.1%at thewavelength of620nm and for the K6[P2W18O62]14H2O P2W18–based EC smart window is48.7%at646nm. The coloration time extracted for a90%transmittance for theP2W17–based EC smart window is0.9s and for the P2W18–based smart window is0.97s;the coloration efficiency for the P2W17–based EC smart window is205.3cm2C–1and theP2W18–based smart window is176.8cm2C–1. Both of the P2W17–and P2W18–based ECsmart windows have the features of remarkable durability over1000cycles. TheP2W17–based smart window has larger optical contrast and higher coloration efficiencythan the P2W18–based smart window. More significantly is the near–infrared behavior ofthe P2W17under different applied potentials was recorded for the first time by using thesmart window. We believe the performance of the P2W17–based smart window is thestate–of–the–art among the POMs–based EC smart windows.