Research On PbS Colloidal Quantum Dot Solar Cellswith ZnO Electron Transport Layer

PbS colloidal quantum dot solar cells?CQDSCs?with heterojunction structure have developed rapidly in recent years,with a certified power conversion efficiency?PCE?of 10.6%and excellent air-stability.However,the light-absorption and carrier-separation compromise,caused by the insufficient diffusion length of photoelectron in PbS quantum dots?QDs?absorption layer,is still the critical factor that limits further improvement of cells efficiency.Moreover,its industrial prospect has also caused concern gradually.PbS nano-ink and new device fabrication process have been reported to realize large-scale production.However,less attention has been focused on electron transport layer?ETL?materials,which can also restrict cell efficiency and industrial prospect.In this paper,several works have been carried out on ZnO electron transport layer to solve above mentioned problems:1.Magnetron sputtering ZnO film has been prepared under low temperature,and used as ETL in PbS CQDSCs.Compared with spin-coated ZnO nanoparticles film,it shows much rougher and pin-hole free morphology,and competitive results of cell efficiency?6%?and air stability have been observed in PbS CQDSCs with planar heterojunction structure.Furthermore,flexible cells were also fabricated with 3.87%efficiency and showed good bending durability.Finally,large-area cells were explored and promising results were observed.In short,magnetron sputtering ZnO film can replace ZnO nanoparticles film as ETL in PbS CQDSCs,and is suitable for large-scale production.2.Temperature is one of important factors that directly affect solar cells performance in actual conditions.Here,we investigated the effect of different ZnO ETL on PbS CQDSCs temperature-dependent properties.PbS CQDSCs with sputtered ZnO and ZnO nanoparticles were fabricated separately.Their current density-voltage?J-V?characteristics in the range from 260 K to 350 K,showed the same decreased trend for open-circuit voltage?Voc?and PCE,and increase trend for short-circuit current density?Jsc?in cells with ZnO nanoparticles,while reverse trend in cells with sputtered ZnO.Temperature-dependent photoluminescence and photoconduction measurements were further carried out and indicated that,different charge transport mechanisms and defects distribution were the major reason for cells different temperature-dependent properties.Therefore,research on ETL is of great importance to promote PbS CQDSCs efficiency improvement and industrialization process.3.We utilized ZnO nanowires to construct PbS CQDSCs with bulk-heterojunction structure,with the aim to solve the light-absorption and carrier-separation compromise through orthogonalization of their directions.As a result,Jsc was significantly improved at the expense of Vocsacrifice.Enhanced interface charge recombination,caused by sharply increased contact area between ZnO and PbS,was attributed to this open-circuit voltage loss.Since increasing the distance between ZnO and PbS can prominently reduce the probability of charge recombination,we introduced an solution deposited ultrathin Mg?OH?₂ interlayer under low temperature.As a result,surface defects on ZnO nanowires were passivated as proved by photoluminescence measurements,and electron lifetime was increased manifold as proved by open-circuit voltage decay measurements.Therefore,Voc increase?33%?and PCE improvement?25%?were finally realized.Statistics result also demonstrated the reliability of this Mg?OH?₂ interlayer in suppressing interface charge recombination.Further tests under various light intensities revealed that,more attention should be focused on the issue of charge recombination in PbS QDs layer to promote PbS CQDSCs further development.