Tuning The Composition-dependent Optical Properties Of Environmental-Friendly Cu-In-S Colloidal Quantum Dots For Optoelectronic Applications

Different from bulk semiconductor materials,the advantage of colloidal semiconductor quantum dots(CQDs)is that the electronic energy band can be regulated by quantum confinement effect and surface effect without changing the material.The excellent performance of the size tunable makes CQDs potential in the application of new nano devices,such as CQDs solar cells(SC),photoelectrochemical cells(PEC),light emitting diodes(QLED)and photodetectors(PD).However,we are in the pursuit of device performance while ignoring the impact on the environment and human health.Nowadays,most of the high-performance optoelectronic devices based on CQDs mainly contain highly toxic heavy metal(like Cd or Pb).The usage of these highly toxic heavy metal elements greatly limits the further development of CQDs.Therefore,it is very important to develop low cost,high-performance and environmental-friendly colloidal quantum dots in the application.Cu In S₂(CIS)CQDs have excellent photoelectric properties,such as high absorption coefficient,near-infrared fluorescence,environmental-friendly and non-toxic.However,due to its narrow tunable bandgap range,it is difficult to meet the needs of various optoelectronic devices.In this dissertation,the environmental-friendly multinary Cu-Zn-In-S(CZIS)and Cu-In-Se-S(CISe S)CQDs with adjustable components are prepared by the alloying Cu In S₂ CQDs with Zn and Se,respectively,and which will widen and narrow the bandgap of Cu In S₂ CQDs,respectively.The optical properties with the composition are further studied.Finally,we fabric the PEC and PD devices by CZIS and CISe S CQDs,respectively,to achieve the environmental-friendly application of CQDs.The research detail is as follows:(1)The CZIS QDs with adjustable composition were synthesized by simple thermal injection method.The CZIS CQDs have good monodispersivity and crystallinity with alloyed chalcopyrite structure.The mount of Zn in the colloidal quantum dots can be adjusted with the bandgaps changes from 2.0 to 2.3 e V.The addition of Zn can effectively passivate the surface defects,thus inhibiting the non-radiation recombination and enhancing radiation recombination.However,excessive addition of Zn can cause serious lattice distortion and more complex defect states,which can lead to more complex non-radiation composite paths and damage the optical properties of QDs.(2)In order to prepare QDs sensitized PEC photoanode,CZIS CQDs were uniformly and tightly deposited in mesoporous Ti O₂ film by a simple,safe,and effective chemical bath deposition(CBD)method.The heterojunction formed between CZIS QDs which had optimized optical properties and Ti O₂ can achieve more effective separation and transfer of photogenerated charge.And as-sensitized PEC cells had the best performance.In addition,the hydrogen generation and stability of the device can be further improved by using 6-layer Zn S passivation layer.(3)The CISe S QDs with adjustable compositions were synthesized by thermal injection method,and the near infrared(NIR)PD were prepared by depositing CISe S QDs in mesoporous Ti O₂ films.The synthesized CISe S CQDs had good crystallinity,with the same chalcopyrite structure of Cu In S₂ and Cu In Se₂.The absorption spectrum of CISe S QDs shifted to red regions with the increase of Se element ratio,and the bandgaps of as synthesized CISe S QDs narrow from 1.40 to 1.17e V.For the NIR PD,CISe S QDs were distributed evenly in mesoporous Ti O₂ films.At the same time,due to the gradual broadening of absorption,the CISe S QDs PD with the optimized Se content had the best photoelectric detection performance.In conclusion,the environmentally friendly multinary CZIS and CISe S CQDs with adjustable compositions and tunable optical properties are prepared by alloying CIS CQDs with Zn and Se,which leads to the broadening and narrowing of the bandgaps of Cu In S₂ CQDs,respectively.Based on this,we have completed the application from materials to devices through the fabrication of two kinds of devices.It also provides a reference for the application of the multinary alloy CQDs and their devices.