Absorption properties enhancement of the photoanode with titanium dioxide nanotubes by deposition of cadmium sulfide via different techniques

Abstract

In recent decades, many scientific studies have been focused on alternative energy sources due to the growing energy needs of the world's population. Solar energy can cover the entire energy consumption of the world population and meet the future energy needs. Although commercial solar cells based on silicon have the efficiency over 20%, the production costs of this type of solar cells are very high. Therefore, in recent years the great efforts of researchers have been focused on the development of a new and cheaper type of solar cells. Among the studied structures there are solar cells sensitized with quantum dots, whose role is to improve the absorption properties of TiO2 photoanode. Compared to organic dyes as sensitizers, quantum dots are cheaper, more stable and show the multiple exciton generation effect. These cells consist of nanoporous TiO2, whose absorption onset is shifted to longer wavelengths by depositing of nanoparticles of selenium and tellurium compounds on the surface of TiO2. Cadmium sulfide (CdS) has a conduction band edge 0.5 eV lower than the conduction band edge of TiO2, which allows the transfer of the excited electrons from CdS to TiO2, preventing the recombination of electrons with photogenerated holes. Since for the effective electron transfer, the direct contact between the TiO2 and sensitizersis essential, thus it is necessary to provide a large specific surface available for sensitization. Among the investigated TiO2nanostructures, that meet the required criteria, it has been shown that nanotubes allow better performance of the final solar cell compared to TiO2 nanoparticle. Onedimensional nanotubes allow rapid transport of excited electrons and reduce the electron energy loss that happens at nanoparticles interfaces...

Poslednjih decenija mnoga naučna istraživanja su fokusirana na alternativne izvore energije usled sve većih potreba svetske populacije za energijom. Solarna energija može pokriti celokupnu energetsku potrošnju svetske populacije i zadovoljiti buduće energetske potrebe. Iako komercijalne solarne ćelije na bazi silicijuma imaju efikasnost i preko 20 %, troškovi proizvodnje ovog tipa solarne ćelije su veoma visoki. Zbog toga su veliki napori naučnika poslednjih godina usmereni na razvoj novog i jeftinijeg tipa solarne ćelije. Među izučavanim strukturama su solarne ćelije sa kvantnim tačkama kao senzivatorima, čija je uloga poboljšanje apsorpcionih svojstava fotoanode na bazi TiO2. U poređenju sa organskim bojama kao senzivatorima, kvantne tačke su jeftinije, stabilnije i pokazuju efekat višestrukog pobuđivanja elektrona. Ove ćelije se sastoje od nanoporoznog TiO2, čija je apsorpciona granica pomerena ka većim talasnim dužinama deponovanjem nanočestica jedinjenja halkogenih elemenata na površini TiO2. Kadmijum-sulfid (CdS) ima granicu provodne zone nižu za 0,5 eV od granice provodne zone TiO2, što omogućava transfer pobuđenih elektrona iz CdS u TiO2, sprečavajući rekombinaciju elektrona sa fotogenerisanim šupljinama. S obzirom na to da je za transfer elektrona bitan direktan kontakt između senzivatora i TiO2 neophodno je da se obezbedi velika specifična površina TiO2 dostupna za depoziciju senzivatora. Od izučavanih nanostruktura TiO2, koji zadovoljavaju traženi kriterijum, dokazano je da nanocevi omogućavaju bolje performanse konačne solarne ćelije u odnosu na nanočestični TiO2. Jednodimenzionalnost nanocevi omogućava ubrzan transport...