Tandem Infrared Photodetector Based On PbS Colloidal Quantum Dots

In recent years,the synthesis of near infrared semiconductor quantum dots?QDs?such as HgTe,InP,PbS,have developed rapidly,especially for the lead chalcogenide QDs?such as PbSe and PbS?since they have unique advantages over other materials.IV-VI colloidal QDs?CQDs?are a kind of direct bandgap semiconductor materials with more obvious advantages,such as quantum size effect,surface effect and multiple exciton generation?MEG?,therefore they can be widely used in infrared photodetector,biological tracers,solar cells,optical fiber communication and so on.Due to the size of the quantum dots can be adjusted by controlling the reaction conditions while the quantum dot size directly affects the absorption peak,thus infrared photodetector based on PbS CQDs responsive spectrum can be adjusted correspondingly.By continuously exploring the synthesis,membrane technology,surface ligand exchange,film thermal annealing process of the PbS QDs as well as by optimizing the device structure,the device performance of PbS-based infrared photodetector?such as the responsivity,the detectivity and the sensitivity,etc.?has achieved great enhancement.Here,in this thesis we tentatively to fabricate novel tandem IR photodetectors based on PbS QD,and we hope it can provide some useful data for high-sensitivity photodetectors and the main conclusions are summarized as following:?1?By using the hot-injection method,we used PbO to act as the source of lead and?TMS?₂S as the source of S,PbS quantum dots with particle sizes about 4nm have been successfully synthesized.O ur experimental data confirmed that the quantum dot size and its absorption peak can be changed by controlling the reaction temperatures and the reaction time.?2?TBAI treatment has been used to increase the interparticle coupling and the carriers'mobilities by replacing the long insulating oleate ligands with shorter and more conductive surfactant molecules,in this way,the device performance has been improved.?3?By introducing the intermediate layer?ZnO/Poly-TPD?,we have fabricated tandem infrared photodetectors ITO/PEDOT:PSS/PbS/ZnO/Poly-TPD/PbS/ZnO/Al,in which the inter-layer provides an effective energy barrier to blocks the currents of holes and electrons,thus to reduce the leakage current and the ZnO/Poly-TPD interface works as the recombination centers allowing the recombination of the carriers.Compared with single infrared photodetector ITO/PEDOT:PSS/Poly-TPD/PbS/ZnO/Al,the responsivity R and the specific detectivity D^*of tandem photodetector are greatly enhanced.Under a 11.7?W/cm²illumination and negative 0.5 V bias,the responsivity R reached 0.3 A/W with the specific detectivity D^*of 2×10¹² Jones for tandem infrared photodetector ITO/PEDOT:PSS/PbS/ZnO/Poly-TPD/PbS/ZnO/Al.