Research On The Light-absorbing Layer And Interface Modification Of Planar Perovskite Solar Cell

Perovskite solar cells(PSCs)are emerging thin-film solar cells in the past 10 years.This remarkable progress is attributed to its exceptional material properties,which include superior light absorption coefficient,low exciton binding energies,long carrier diffusion lengths and solution processing.The role of perovskite materials is to absorb photons to produce photo-generated carriers.For PSCs devices,one of the key issues limiting the photoelectric conversion efficiency(PCE)of cells is the crystalline quality of the perovskite light-absorbing layer.Many excellent properties exist in effective and stable perovskite materials,including capturing sufficient light,reducing the generation of deep recombination centers,reducing non-radiative recombination,and improving charge transfer efficiency.Ultimately,the performance of PSCs is improved.In addition,the materials between the two interfaces also play an important role in device performance.The two materials,which have matching energy levels,facilitate the extraction and transmission of electrical charges.Therefore,how to obtain an excellent perovskite light-absorbing layer and a more suitable interface material is a problem to be solved in the preparation of high-efficiency perovskite solar cells.For the quality of the perovskite light absorption layer and the interface material,the crystal quality and morphology of the perovskite thin film are effectively controlled mainly through additive engineering in this paper.At the same time,the influence of interface modification on the PCE and hysteresis of PSCs was studied.The specific research contents are as follows:1.Gallium(Ga)ion-doped tin oxide(SnO2)serves as an electron transport layer.Most planar PSCs suffer from current-voltage hysteresis,which derives from interface mismatch,surface defects,ion migration,and ferroelectric property et al.Doping Ga into the SnO2 nanocrystal electron transport layer by a low-temperature solution method to reduce the hysteresis effect in PSCs.It is revealed that the Ga-doped SnO2 electron transport layer owning better band alignment with the perovskite absorption layer,which is helpful for electron extraction.It is found that Ga doping severely decreases the trap state density in SnO2,leading to a lower recombination rate and reducing hysteresis.With the optimized doping concentration of Ga ions,the champion device achieves a highest PCE of 18.18%and the hysteresis index is reduced from 23.9%to 1.7%.This doping method significantly reduces the current-voltage hysteresis in PSCs.The characteristics of this method include simple process and low cost,which lays the foundation for the commercial application of PSCs.2.Nicotinamide(NTM)modified(FAPbI3)0.97(MAPbBr3)0.03 was used as the light absorption layer.Perovskite films with excellent crystallinity and crystallite size are essential for efficient and stable PSCs.The trap states in perovskite films have been proven to be effectively passivated by Lewis acid or base functional groups.In this work,NTM serving as a Lewis base additive is introduced into the PbI2 or FAI:MABr:MACl precursor solution to obtain NTM-modified perovskite films.It has been found that the NTM in the perovskite film can well passivate surface and GBs defects,control the film morphology and enhance the crystallinity via its interaction with a lone pair of electrons in nitrogen(N).NTM has a coupling effect with Pb and I ions in perovskite through its own amino and pyridine functional groups,which increases the activation energy during thin film crystallization.In the presence of the NTM additive,we obtained perovskite solar cells with a grain size of about 2 microns and stabilize efficiency of 21.7%.Molecules with amino and pyridine functional groups are added to the perovskite light-absorbing layer to obtain a perovskite film with excellent quality.This discovery provides a new tactic for the preparation of high-quality perovskite light-absorbing layer.3.Choline chloride modified(FAPbI3)0.97(MAPbBr3)0.03 was used as the light absorption layer.Passivation of defects on the surface and at grain boundaries of perovskite films has become one of the most effective strategies to suppress charge recombination in perovskite solar cells.By adding different concentrations of choline chloride to the PbI2 precursor solution,a dense,pinhole-free(FAPbI3)0.97(MAPbBr3)0.03 light-absorbing layer was prepared.Passivating the defects of perovskite film by choline chloride improves the quality of the film.Effective defect passivation reduces the charge trap density and extends the carrier life.As a result,the open circuit voltage(Voc)of the PSC is increased to 1.17 V.When the amount of choline chloride added was 90 mM,the PCE of the PSCs increased from 19.33%to 22.31%.Compared with the general method of Lewis acid or base passivation of perovskite film defects,this method shows better PCE.It provides new idea for the preparation of high-performance PSCs.