Suppression Effect of MgO Nanoparticles on Carrier Recombination in ZnO Ultraviolet Photoelectric Conversion Coatings
Mixed oxides are extensively utilized in the solar cell development due to their beneficial properties.For instance,MgO is commonly incorporated into electron transport layers that shows significant carrier recombination,helping to suppress this recombination and enhance the Photoelectric Conversion Efficiency(PCE).Furthermore,ZnO finds the widespread application in sensors and various types of solar cells.In silicon-based solar cells,ZnO nanostructures can enhance the absorption of the blue-ultraviolet spectra,thereby improving their fill factor and PCE.However,the oxygen vacancies(Vo0,Vo+,Vo2+)in ZnO can create recombination centers,negatively affecting its n-type semiconductor properties.Therefore,addressing these defect-induced recombination centers is crucial.This study investigated the incorporation of MgO nanoparticles into ZnO to create a homogeneous mixture.The mixed powder was dispersed in an ethanol solution and subjected to the ultrasonic agitation,resulting in a uniform suspension of the nanoparticles.After adding a small amount of thickening agent,the suspension was spin-coated onto the emitter surface of a p-type Passivated Emitter and Rear Cell(PERC).The nanoparticle coating was then solidified through a high-temperature annealing.To ensure a direct contact between the nanoparticle coating and the emitter,a"semi-finished"PERC cell without a front-side SiNx layer was used as the substrate.This semi-finished cell has a slightly lower PCE of approximately 17.1%compared to the fully finished cells.During the film preparation process,the electrical properties of the mixed nanoparticle coating were optimized using the control variable method.Variables such as the ratio of mixed nanoparticles,the concentration and viscosity of nanoparticles in the spin-coating solution,the spin-coating speed,and the curing temperature were adjusted to address the issue of poor electrical stability in the nanoparticle coating.The current-voltage curves of the solar cell samples,measured before and after applying the coating,revealed that substrate cells with the ZnO-MgO nanoparticle coating exhibited a higher short-circuit current density under illumination.Additionally,the ZnO-MgO nanoparticle coating increased the overall PCE of the solar cell from 17.10%to 19.22%,representing a 4.68%improvement compared to the PCE of the use of ZnO nanoparticles alone(18.42%).This indicates that the ZnO-MgO nanoparticle coating provides a superior enhancement in the electrical performance of the solar cells.The Hall effect measurements further showed that the ZnO-MgO nanoparticle coating resulted in a higher carrier concentration and a slower decay of photogenerated current after the light exposure,suggesting that the carrier recombination processes were effectively suppressed.The nano-spherical morphology of ZnO-MgO nanoparticle coating on the textured emitter surface also exhibited light-trapping effects,further enhancing the light absorption and improving the PCE.Furthermore,the excitation spectrum analysis indicated that the addition of MgO nanoparticles facilitated the electron transport and reduced the recombination speed within the ZnO nanoparticle coating,significantly lowering the peak intensity of the excitation spectrum.From a structural perspective,the microstructure of the ZnO-MgO nanoparticle coating exhibits a light-trapping capability,forming a layer of spherical particles ranging from 30 to 70 nm in diameter on the solar cell emitter surface.This layer enhances the light absorption capacity of the substrate solar cell,particularly in the ultraviolet and visible spectra regions,due to the combined contributions of ZnO and the substrate.Additionally,the incorporation of MgO effectively suppresses the charge recombination,leading to the enhanced optical and electrical performance of the solar cells.Thus,the use of ZnO nanoparticles alone resulted in a 1.32%increase in the PCE,whereas the combined effect of ZnO and MgO nanoparticles yielded a 2.12%PCE improvement compared to that of the substrate.These results demonstrate that the ZnO-MgO nanoparticle coating not only optimizes the light absorption and the carrier concentration,but also reduces the carrier recombination,thereby meeting the solar cell's requirements for the enhancement in minority carrier lifetime.This research provides new insights and potential applications for the development of next-generation solar cells.
Solar cellsUltraviolet photoelectric conversionNanoparticleZnOMgOCarrier recombinationSuppression effect
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