Study On The Interfacial Electron Transfer Behavior Of CuSe/CuS Composite Counter Electrode In Quantum Dots Sensitized Solar Cells

Supervisor:Prof.Tengfeng Xie Specialty:Physical ChemistryAs a kind of third generation solar cell,quantum dots sensitized solar cells?QDSCs?have been drawn widely attention due to its cost-effective and simple preparation process.According to pervious report,the highest photoelectric conversion efficiency?PCE?of QDSCs has reached a record of 13.34%.However,it is still lower than the theoretical PCE?66%?.Besides,it also could not meet the request of commercial manufacture and commercial application.Hence,it is a hot spot of exploring new electrode materials and electrolytes to further improve the photoelectric performance of QDSCs.In addition,the counter electrode?CE?services as a part of the conventional QDSCs.Hence,it is an important way of preparing CE with the outstanding performance for the enhancing photovoltaic performance of solar cell.Recently,the composite CE material has been attracted more attention,because it could combine the various excellent performances of single counter electrode material.However,the introduction of variety kinds of CE materials could increase the interfacial electron transport in composite CE,leading to the reduction of its electron transport performance.Therefore,the problem is how to reduce interfacial electron transport resistance in the composite CE material.For the above mentioned problems,in this paper,CuSe/CuS heterojunction is prepared to promote the electron transfer from CE to electrolyte in composite CE.It could reduce the interfacial electron transport resistance of CE,enhance the electrocatalytic activity of CE and increase the overall photoelectric conversion efficiency of solar cell.In addition,the interfacial electron transport behavior of CuSe/CuS heterojunction composite CE could be further studied by electrochemical analysis method,Kelvin probe technology,transient photovoltage technology,transient photocurrent technology,and so on.The specific work contents are divided into the following two parts:1.To understand the interfacial electron transport behavior of CuSe/CuS heterojunction CE,we prepare CuSe/Cu_xS composite CE by depositing Cu_xS on FTO with chemical bath deposition method followed by screen printing CuSe slurry on Cu_xS/FTO.The interfacial energy band structure of the heterojunction between CuSe and Cu_xS could be adjusted by the Cu/S rato of Cu_xS in CuSe/Cu_xS composite CE.It is found that the enhancing interfacial bulid-in field of heterojunction in CuSe/Cu_xS CE could promote electron transport from CE to electrolyte when the Cu/S rato of Cu_xS increasing from 0.52 to 0.78,leading to the decreasing interfacial barrier of heterojunction,the reducing resistance at solid-solid interface and enhancing electron transport performance of composite CE.Finally,the QDSCs based on CuSe/Cu_0.78S CE shows the outstanding photoelectric conversion efficiency of 5.70%,which is higher than that of the cell with CuSe CE?4.82%?and Cu_0.78S CE?4.13%?.However,the reverse interfacial bulid-in field of heterojunction in CE makes against the electron transport in CE,accounting for the decreasing electron transport performance of composite CE and the decreasing photoelectric conversion efficiency of QDSCs?4.65%?.2.In order to further enhance the catalytic activity and electron transfer performance of CE for the improving PCE of QDSCs,two improving programs towards the preliminary work should be pointed out:?1?Increase the superficial active sites?decrease the electron transfer resistent of the solid-liquid interface?for enhancing electrocatalytic activity of composite CE;?2?Reduce interfacial defects of heterojunction?decrease the electron transfer resistent of solid-solid interface?for strengthening the interfacial electron transport of composite CE.For these two aspects,we pretreat the brass with the hydrochloric acid as a growingsubstrate,following by fabricating the Cu_2-xSe/Cu₂S composite CE beased on the growing substrate by in situ sacrificial template method.It could found that,on the one hand,after treating with hydrochloric acid,the brass sheet shows the porous structure of surface,which could increase the surface active site of CE towards electrolyte,readuce the interfacial electron tranfer resistance at solid-liquid interface and enhance the electrocatalytic activity of Cu_2-xSe/Cu₂S CE.On the other hand,the Cu_2-xSe/Cu₂S CE shows the higher breakdown voltage?0.75 V?as compared to CuSe/Cu_0.78S CE?0.19 V?,which indicating its inner strengthened heterojunction.It is more benefitcial of electron transfer from Cu₂S to Cu_2-xSe at solid-solid interface in CE,leading to the decreasing interfacial electron tranfer resistance at solid-solid interface and enhancing electron transfer performance of Cu_2-xSe/Cu₂S CE.Eventually,the QDSCs based on it achieves the outstanding photoelectric conversion efficiency of 6.10%.