Study Of NIR Long Afterglow Luminescent Materials Are Used In Silicon Solar Cells To Produce Electricity Under Dark Condition

Universally,the silicon solar cells can realize effective photoelectric conversion only under sunlight irradiation,and that can not generate electricity under dark condition.Thus,the effective working（photoelectric conversion）time of silicon solar cells throughout the whole day is very limited.Therefore,it is a challenge to make silicon solar cells generate electricity in all kinds of sunlight and weather conditions,even darkness.In recent years,some researchers have used generally require certain technical means to combine long afterglow luminescent material and Ti O₂forming a thin film,and then load it on FTO glass to form a new composite photoanode.So as to form solar cells that can generate electricity under no light conditions.Although the generation of afterglow current was realized to a certain extent,this method has some limitations.For example,the stability of the original solar cell was damaged to a certain extent,the production cost was increased,and the visible light transmission of the composite photoanode was reduced.Therefore,the near infrared（NIR）long afterglow luminescent materials,Zn₃Ga_2-xGe₂O₁₀:x Cr³⁺with different Cr³⁺concentration and different calcination temperatures,were successfully prepared through high temperature calcination method.At the same time,a series of up-conversion NIR luminescent phosphors,Zn₃Ga_1.99-y-zGe₂O₁₀:1.0Cr³⁺,y Yb³⁺,z Er³⁺,were also received by incorporating Yb³⁺,Er³⁺and Yb³⁺-Er³⁺pairs into Zn₃Ga_1.99Ge₂O₁₀:1.0Cr³⁺sample.Firstly,The structure,morphology and elemental composition of the prepared materials were investigated,respectively,by X-ray powder diffraction（XRD）,scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,X-ray elemental mapping spectroscopy（EDS）,X-ray energy spectroscopy（EDX）and X-ray photoelectron spectroscopy（XPS）.In addition,their optical properties including emission wavelength,afterglow intensity and luminescent time were studied by photoluminescence（PL）spectroscopy and up-conversion luminescence（UC PL）spectrum.It was confirmed that a wide band emission peak 600 nm-850 nm in the near infrared region of the fluorescence emission spectrum was found,which was caused by ionic transition of Cr³⁺.In addition,Zn₃Ga_1.99-y-zGe₂O₁₀:1.0Cr³⁺,y Yb³⁺,z Er³⁺phosphors can be excited by near infrared light at 980 nm.And after that,the up-conversion emission peaks of Er³⁺and Cr³⁺were discovered.This indicates that there is an energy transfer process between Cr³⁺and rare earth ions.The silicon solar cells with“Hinge”structure were obtained,respectively,by fixing the above-mentioned luminescent materials on a glass sheet and then combined with silicon solar cells.Additionally,the influences of doping proportions of Cr³⁺,Yb³⁺,Er³⁺,Yb³⁺-Er³⁺pairs and calcination temperatures at night power generation of the round-the-clock silicon solar cells were discussed.The results indicate that the photoelectric conversion efficiency of silicon solar cells combined with Zn₃Ga_1.975Ge₂O₁₀:1.0Cr³⁺,1.0Yb³⁺,0.5Er³⁺is reached the maximum value of 2.549%under dark condition.At the same time,the silicon solar cell can generate dark current for up to eight hours,with maximum dark current density and open-circuit voltage of4.883μA/cm²and 0.914 m V,respectively.It is hoped that this study can provide some new ideas for silicon solar cells to generate electricity without sunlight irradiation.