The Applications Of Polyoxometalates-based Inorganic Photosensitizers In The P-DSSCs

Recently,energy crisis is becoming more and more serious.Among all kinds of photovoltaic devices,dye-sensitized-solar-cells?DSSCs?is one of the most promising devices for their advantages,such as low cost,ease fabrication and high power conversion efficiency?PCE?,so DSSCs has attracted a growing numbers of attention.p-type dye-sensitized-solar-cells?p-DSSCs?which can convert light into electricity is an important branch of DSSCs.Photosensitizers is the key part in p-DSSCs,but the high price of photosensitizers hinder p-DSSCs' application.So it's crucial in p-DSSCs commercialization to replace the photosensitizers consisted of precious metals or organic molecules by designing and developing new low-cost sensitizers.So developing low cost p-type sensitizers is the urgent matter.Polyoxometalates?POM?are a group of green and atoxic inorganic materials which are prepared by conventional synthesis or hyderthermal synthesis based on chemical elements such as Mo and W et al.Some POM such as TMSPs et al even have excellent optoelectronic properties:they have a far better thermal stability than most photosensitizers;they can can undergo reversible multielectron redox transformations without any significant structural alteration under mild conditions;they have good absorption curves in UV-vis spectrum;some POM also have proper HOMO and LUMO which properly meet the requirements of p-type photosensitizers.So TMSPs et al have the huge potential to be used as p-type sensitizers.In this paper,Keggin-type transition-metal substituded polyoxometalates?TMSPs?,Dawson-type TMSPs and organic carboxylic acid group modified Lindqvist-type POM were used to serve as sensitizers in p-DSSCs and were primarily studied.1.The potential of three Keggin-type transition metal-substituted polyoxometalates,TBA8Na2[SiW9O37{Co?H2O?3}]·1H2O?SiW₉Co₃,TBA stands for?n-C4H9?4N+?,TBA4[?SiO4?W10Mn?2O36H6]·1.5CH3CN·2H2O?Si10M?2?,and TBA3.5H5.5[?SiO4?W10Mn?/?2O36]·10H2O·0.5CH3CN?SiW10Mn?/?2?has been explored as pure inorganic dye photosensitizers for p-DSSCs.SiW₉Co₃-sensitized solar cells scored Voc=81mV,Jsc=1.60mA/cm2,FF=0.30,PCE=0.038%;SiWioMn?2-sensitized solar cells scored Voc= 79 mV,Js=1.28 mA/cm2,FF=0.29,PCE=0.029%;SiW10Mn?/?2-sensitized solar cells scored Voc=93mV,Jsc=0.88 mA/cm2,FF=0.34,PCE=0.027%.All of which are higher than that of coumarin 343?0.017%?.These polyoxometalates are the first three pure inorganic dyes reported for use with p-DSSCs and therefore demonstrate a new strategy for designing photosensitizers,especially pure inorganic dyes.Moreover,they broaden the range of applications for polyoxometalates.2.For the first time we introduce two low cost Dawson-type TMSPs,?2-K8P2W17O61?Co·OH2?·16H2O(P₂W₁₇Co)and?2-K7P2W17O61?Mn·OH2?·12H2O(P₂W₁₇Mn),in the p-PSSCs to be the photosensitizers.We have explored the thermal stability,UV-Vis absorbance spectra,LUMO and HOMO energy levels of the two inorganic photosensitizers.P₂W₁₇Co-sensitized solar cells scored Voc=101mV,Jsc=1.285mA/cm2,FF=0.313,PCE=0.0406%;P₂W₁₇Mn-sensitized solar cells scored Voc=84mV,Jsc=1.268mA/cm2,FF=0.296,PCE=0.0315%.But there comes an encouraging result,P2Wi7Co/P₂W₁₇Mn-sensitized solar cells scored Voc=102mV,Jsc=1.49mA/cm2,FF=0.305,PCE=0.0464%when they are used as the cosensitizers.This is the first try that Dawson-type TMSPs are used as photosensitizers and cosensitizers in low cost p-DSSCs and points out a new potential direction for POM application in energy field.3.A Lindqvist-type POM TBA2[Mo₆O₁₉]and a organic carboxylic acid group modified Lindqvist-type POM TBA2[Mo6O18-?N-C6H4-3-COOH?]were introduced in p-PSSCs for the first time.TBA2[Mo₆O₁₉]-sensitized solar cells scored Voc= 76 mV,Jsc=0.266 mA/cm2,FF=0.241,PCE=0.00486%.While,TBA2[Mo6O18-?N-C6H4-3-COOH?]-sensitized solar cells got Voc=101mV,Jsc=0.648 mA/cm2,FF=0.305,PCE=0.0200%.Compared with TBA2[Mo₆O₁₉]-sensitized solar cells,TBA2[Mo6O18-?N-C6H4-3-COOH?]-sensitized solar cells' Voc,Jsc,FF and PCE were improved 311.5%,32.9%,143.9%and 26.6%,respectively.This demonstrates that carboxylic acid group may help the photosensitizers be absorbed on the NiO electrode and holes' injection between photosensitizers and the NiO electrode.Otherwise,modified Lindqvist-type POM TBA2[Mo6O18-?N-C6H4-3-COOH?]has a stronger light harvesting ability.