| Perovskite Solar Cells（PSC）have received extensive attention since 2009.Due to the excellent photoelectric properties of perovskites,such as high extinction coefficient,long electron and hole diffusion length,the efficiency of PSCs have exceeded 22%.However,PSC is also facing some problems at the same time.Though,the highest efficiency of PSCs is close to that of commercial monocrystalline silicon cells（25%）,such an value is still far below the theoretical limit efficiency of PSCs（32%）.In addition,perovskites degrades under humidity and exhibit inner ion migration phenomenon,the stability of the corresponding device is in urgent need of improvement.What’s more,the current understanding of the photophysical properties of perovskite is still insufficient,which limits their further applications.In view of the above problems,for the first time,this paper proposes that by using spectra-matched aggregation induced emission（AIE）material as the down conversion coating of PSC,the response of PSC to ultraviolet light can be enhanced and the performance of the device can be improved.In addition,the coating can also be used as an encapsulation layer for PSC and improve the stability of the device remarkablely.We have also pointed out the basic conditions to be satisfied to improve the spectra response of photovoltaic device by down-conversion:（1）The down conversion material must have a sufficiently high quantum yield;（2）The absorption and emission spectra of the down conversion material must be well-matched to the spectral response characteristic of the devices,which means the spectrum with lower responsivity for the device can be down-converted to spectrum with a higher degree of responsivity;（3）The light scattering effect of the down-conversion coating in the response region of device should be as small as possible to avoid the loss of incident light.In addition,considering the high quantum yield and excellent film-forming properties of AIE materials in aggregation state,we introduce a typical AIE molecule into perovskite system to study the the photophysical properties of perovskite and the energy and charge consfer between AIE molecule and perovskite.For the first time,we found that CH3NH3PbI3 polycrystalline film exhibits double PL peaks under high-energy and high photon flux laser excitation(3.82 eV,4.08×1022 cm-2 s-1).We attribute the high energy peak and the low energy peak to the recombination of free carriers（FCs）and bond excitons,respectively.The introduction of AIE molecule changes the intensity ratio of two peaks,indicating AIE molecule can change the recombination ratio of FCs and bond excitons in CH3NH3PbI3.These findings not only help to further understand the complex carrier recombination behavior in perovskite,but also provide a new method for studying and adjusting the photophysical properties of perovskite. |
