The Study Of An Internally Photoemitted Hot Carrier Solar Cell Based On Organic-inorganic Perovskite

In recent years,organic-inorganic hybrid perovskite materials,as a highly concerned optoelectronic material,have demonstrated their excellent properties in many fields.For example,the efficiency of perovskite single-cell solar cells has exceeded24%,which is close to the best performance of monocrystalline silicon solar cells;light-emitting quantum efficiency of perovskite electroluminescent devices exceeds10%.Perovskite materials also have superb performance in the field of detector and catalysis.These high performance devices benefit from the excellent carrier properties of perovskite materials:carriers are quickly excited?high absorption coefficient?;long carrier lifetime?long diffusion length?;carriers are less likely to be captured by defects?high defect tolerance?,and so on.Among them,the excellent characteristics of hot carriers in perovskite with long cooling time and long migration have attracted the attention of researchers.Hot carriers in semiconductor materials generated via exciting will relax to the edge of the bandgap through emitting phonons.This process will lose a large amount of energy,thereby limiting the photoelectric conversion efficiency of solar cells.If the energy of hot carriers in the perovskite before relaxation to the band edge can be used to convert it into current,the photoelectric conversion efficiency of the perovskite solar cell will be further improved.At present,the research of hot carriers in perovskite mainly relies on ultra-fast pump-detection technology.In this paper,we propose a new idea to explore hot carriers in perovskite:that is,screen electrons hot and cold electrons in perovskites by constructing a new structure of the device.The aim of this device is to realize the direct utilization of the energy of hot carriers in perovskite under steady-state conditions.The content of this paper includes the following sections:1.To begin with,we review in brief the concept of hot carriers,relaxation theory,the working mechanism of hot carrier solar cells,and the current status of research on hot carriers of organic-inorganic hybrid perovskite materials:ultrafast pump-detection studies have revealed that the hot carrier relaxation rate in perovskite materials is much slower than that of other semiconductor materials,confirming that organic-inorganic hybrid perovskite is a suitable candidate for hot carrier solar cells.2.Based on the investigation of research status at home and abroad,we propose a novel structured device:An internally photoemitted hot carrier?IPHC?solar cell based on organic-inorganic perovskite?FTO/TiO₂/Au/MAPbI₃?,which aims to apply directly the energy of hot carriers in perovskite under steady-state illumination conditions.And then through interfacial modification and doping to further enhance the efficiency of the IPHC device.3.The surface state of perovskite will lead to the electron-hole capture/deposition process,resulting in the loss of photogenerated carrier energy.Therefore,we consider using interface modification to passivate the defect state on the perovskite surface to further improve the ability of IPHC device to collect hot electrons:a simple and efficient method of adding LiF surface modification layer was applied onto the outmost perovskite layer that benefits both reduction of the trap states and formation of interface dipoles.The formation of the interface dipole?MAPbI₃/LiF?promotes the accumulation of perovskite.The electrons move towards the Au/MAPb I₃ interface,and more electrons have a chance to be scattered again.Finally,the IPHC device with Li F modification layer shows a remarkable increase of the short circuit current density with a 20.31%increment.4.Schottky barrier will be formed by contacting the perovskite layer with a high work function Au layer.It is one of the factors limiting the collection of hot electrons by IPHC devices.So,we try to reduce the potential barrier caused by band bending at the MAPb I₃/Au interface through p-type doping:sodium iodide?NaI?is added into the MAPb I₃ precursor solution for preparing p-type perovskite film.The obtained p-type film and the adjustment of its work function lower the energy barrier at the interface of Au/MAPb I₃,leading to more hot electrons extraction and enhanced power conversion efficiency.