High Efficient CdSeTe Quantum Dot Solar Cells

As one of the new generation solar cells,quantum dot sensitized solar cell?QDSC?has shown great potential due to the outstanding advantages of semiconductor quantum dots?QDs?,such as high absorption coefficient,quantum size effect and multiple excition generation?MEG?,which makes it possible to boost the power conversion efficiency beyond the traditional Shockley-Queisser.In the past five years,QDSCs have been developed significantly along with the deeper understanding for the working mechanism of QDSCs and technological progress,and the PCE up to 12% has been achieved.However,the cell efficiency of QDSCs still lags behind other new generation solar cells,such as perovskite solar cells and organic solar cells,and there are still many challenges to further improve the cell performance of QDSCs.As the sensitizer of QDSCs,QD's photoelectric property,synthetic method,surface defects,chemical stability as well as the deposition method on metal oxide have considerable inflence on the cell performance.Moreover,serious interfacial charge recombination is also the key factor to limit the performance of QDSCs.To improve the efficiency of QDSCs,CdSeTe alloyed QD has been used in our work,and a series of works about TiO₂ photoanode structure,charge transport mechanism,and improvement of electrolyte have been carried out as follows:Firstly,high quality CdSeTe colloidal QDs have been prepared by one-pot non-injection method,subsequently adsorbed onto TiO₂ mesoporous film after ligand exchange.The cell performance based on different TiO₂ photoanode structures has been studied,and up to 7.55% of PCE has been obtained by optimizing the photoanode structures,which is one of the highest PCEs at the time.Besides,interfacial charge transfer and transport processes have been systematically investigated by electronchemical impedance spectra?EIS?and open-circuit photovoltage decay?OCVD?.As we know,the performance of QDSCs has been restricted by serious charge recombination.Thus,fumed SiO₂ nanoparticles?NPs?have been introduced into the polysulfide electrolytes to optimize cell interface,decrease interfacial charge recombination and improve cell performance.Fumed SiO₂ NPs can be easily dispersed into polysulfide electrolyte to form stable colloidal,the results show that the open-circuit voltage?Voc?and fill factor?FF?of the QDSCs based on Si O₂ additive have been significantly improved,ultimatedly,the cell efficiency is improved from 8.7% to 11.23%,which is one of the highest efficiency for QDSCs.In addition,the interfacial electron transport and recombination processes were also been investigated,it turned out that some SiO₂ NPs can be deposited on the surface of TiO₂/CdSeTe and form a energy barrier,which can decrease the charge recombination between CdSeTe/TiO₂ and electrolyte,and improve the electron collection efficiency and electron lifetime.This work provides a simple and efficient way to enhance the performance of QDSCs.Besides,the initial exploration for CdSeTe QDs based solid-state quantum dot solar cell has also been carried out.Firstly,CdSeTe QDs were adsorbed on TiO₂ surface with varies of crystal phases?anatase,rutile or mixture?,and the interfacial charge transfer between CdSeTe and TiO₂ has been studied by time-resolved photoluminescence decay spectra and transient absorption spectra.Then the solid-state quantum dot solar cells with the structure of FTO/TiO₂/CdSeTe/Hole transport layer?HTL?/Au have been fabricated,and the difficulty and the key factor are the selection of the depositing way of QDs and the species of HTL.Only a small amount of CdSeTe QDs have been deposited due to a limited thickness of TiO₂ film,which causing low Jsc?0.21 mA/cm2?and cell efficiency?0.06%?.