Effect Of Doping And Surface Capping For The Optical-Electrical Properties Of InP Quantum Dots

InP quantum dots(QDs)exhibt many promising applications due to the various intrinsic advantages,such as Cd-free,narrow bandgap,high absorption coefficient,non-toxicity,good biocompatiablity and easy solution processability.However,the surface defects and dangling bonds of InP QDs are seriously affect the photoluminescence and photoelectrical properties.Doping or surface capping may be the effective methods to reduce the surface defects and improve the optical properties of InP QDs.In this dissertation,we focused on the synthesis of novel doped InP QDs,the luminescent properties and photoelectricity performances as the absorption materials of the QDs sensitized solar cells.The detailed contents are described as follows:1.The Li,Zn and Sn doped InP QDs(named Li:InP,Zn:InP and Sn:InP)are firstly synthesized by one-pot in-situ nucleation-doping approach,and as-synthesized QDs possess high crystallinity and good size distribution.The optical performances of these doped InP QDs are studied in detail.As a result,the absorption and photoluminescence spectra of InP QDs obviously blue shift with the increase of Li,Zn dopant concentration,while it’s inverse for Sn doped InP QDs.In addition,the relative photoluminescence intensity of Li:InP and Zn:InP QDs are obviously higher than that of undoped InP QDs,which is favor for the synthesis and applications of short wavelength luminescent(such as green and blue)QDs.2.High efficient Li:InP,Zn:InP and Sn:InP quantum dot sensitized solar cells(QDSSCs)are firstly obtained by capping ligand-induced self-assembly(CLIS)approach.The high efficient Sn:InP QDSSCs are obtained because of broad absorption and high loading of QDs.Moreover,the effects of ligand exchange efficiency,thickness of photoanode films and Sn dopant concentration for the cells’performances are also systematically investigated.As a result,the InP and Sn:InP QDSSCs reached PCE of 2.5%and 3.5%under AM 1.5G illumination of 100 mW/cm~2,respectively,which are the highest PCE for III-V cluster QDSSCs.3.High luminescent Ga doped InP(named Ga:InP)QDs are synthesized via a growth-doping method,and the photoluminescence and solar cell performances are investigated.The experimental results show that the as-synthesized Ga:InP QDs possess narrow size distribution,high crystalline and high photoluminescence yield.By optimizing the reaction conditions,such as the growth temperature and dopant concentration,the quantum yield of Ga:InP QDs reaches 14%,which is obviously enhanced than that of the undoped InP QDs.Also,we prepared the Ga:InP QDSSCs by CLIS approach,and an enhanced cell efficiency of 2.8%is obtained.This enhancement may be come from the surface passivation of InP QDs by Ga ions.4.Based the surface passivation of InP QDs,we constructed several Type-I core/shell QDs,such as InP/ZnS,InP/ZnSe,Ga:InP/ZnS and Ga:InP/ZnSe,and investigated their performances of photoluminescence and QDSSCs.Results show that capping with wide bandgap semiconductor shell can obviously improve the open circuit voltage.PCE for Ga:InP/ZnS and InP/ZnS core/shell QDSSCs cell device are 4.2%and 4.7%under AM1.5G illumination of 100 mW/cm~2,respectively.