Study On The Exciton Dynamic Processes In Cdse Semiconductor Quantum Dot Thin Films And Its Photovoltaic Devices

Solar power as a kind of clean, renewable energy has been received extensiveattention. In recent years, the new generation solar cells with high efficiency (alsoknown as the third generation) which put the applications of variety of newnano-materials and the research of new structure as the starting point is becominga research hotspot. Compared with conventional solar cells, the new generationhigh efficiency solar cells not only maintain the advantage of environmentalprotection and low cost characteristics of the thin film solar cells, but also cansignificantly improve the photoelectric conversion efficiency of solar cells. Thispaper is intended for the new generation solar cells based on multiple excitonseffect in quantum dots, and studies the exciton dynamic processes in thesemiconductor CdSe quantum dots and its photovoltaic devices.This paper firstly studies the preparation technology of CdSe quantum dot thinfilms and its photovoltaic devices; the experimental conditions and theexperimental method of the preparation of CdSe quantum dot thin films and itsphotovoltaic devices are confirmed. Dip-coating method was applied to preparcolloidal CdSe quantum dots into CdSe quantum dot thin films with the ITO glassas the substrate. the structure, basic principle and properties of various kinds ofmaterials used for preparation of organic double heterojunction solar cell inexperiments are interpreted; and the whole preparation process of CdSe quantumdot photovoltaic devices with structure of ITO/PEDOT: PASS/CdSe(QDs)/PCMB/Al is introduced, using the spin coating method, dip-coating method, and vacuumevaporation technique.Secondly, the ultrafast spectroscopy and photoelectric characteristics testingsystem are introduced. In this paper, the study of exciton dynamic processes inCdSe quantum dots uses the femtosecond time-resolved transient absorptionultrafast spectroscopy and picosecond time-resolved fluorescence ultrafastspectroscopy. Then, therefore, the basic principle of two kinds of spectrumtechnique and testing methods above is learned and researched, as well as for thebasic principle and testing method of transient photocurrent and photovoltagespectrum testing technique to CdSe quantum dots in the photovoltaic devices.Finally, using the relevant experiment system, CdSe colloidal quantum dots,coupled CdSe quantum dot films and CdSe quantum dot photovoltaic devices asthe research object, the untrafast dynamic processes of biexciton relaxation，surface trapping in quantum dots etc. in the isolated quantum dots and coupledquantum dots are mainly studied, as well as the exciton-split dynamic process in photovoltaic devices. Absorption spectroscopy and fluorescence spectroscopy ofthe CdSe colloidal quantum dots and its films are respectively analyzed.Comparedthe differences between them, the conclusion that blue shifting of absorption andfluorescence spectroscopy of CdSe quantum dot films in contact with air which isexcited by the laser are obtained. Based on the fitting analysis of time-resolvedtransient absorption spectroscopy and time-resolved fluorescence spectra testingdata of the CdSe colloidal quantum dots and its films, the influence mechanism ofsurface trapping effect to the lifetime of excitons is confirmed. And the dynamicmechanism of the excitons from production to the final recombination in the CdSequantum dots is confirmed. Also through analyzing the differences between them,the conclusion that there is strong coupling between the quantum dots which areprepared into films and packed together closely and the charge will transferbetween the mutual coupled quantum dots is obtained. At the same time, thephotovoltage spectroscopy and transient photocurrent of the CdSe quantum dotphotovoltaic devices are studied. Through using the photovoltage spectroscopyand transient photocurrent texting technique, The photoelectric and photovoltageproperties of the CdSe quantum dot photovoltaic devices are known, and theexciton-split dynamic processes in photovoltaic devices and interface chargetransfer are confirmed.