Optoelectronic Performance Enhancement By Incorporating Plasmon Effect Into Perovskite Solar Cells

In recent years,the power conversion efficiency?PCE?of organic-inorganic halide perovskite solar cells?PSCs?has increased from 3.8%to 23.25%currently.However,the separated electrons and holes need to be collected by their respective electrodes before they recombine,and thethickness of active layer is usually among 400 nm to ensure the absorption length?1/??exceeds the minority carrier diffusion length.However,the thinner absorbing layer may cause the incident light cann't be totally absorbed,which can result in a low power conversion efficiency?PCE?of the PSCs.In addition,it is a great challenge to utilize the incident light and ultimately obtain a high PCE in the resulting PSCs.At present,there are many approaches to increase light absorption in solar cells,such as the using of photonic crystals,plasmoic nanoparticles and coated anti-reflection films,among which,the local electric field generated by the surface plasmon resonance?SPR?of plasmonic nanoparticles is used to enhance the absorption of incident.In PSCs,metallic nanoparticles are mainly incorporated into the absorber layer or the hole transport layer bulk to utilize its SPR effect.However,the incorporation of metallic nanoparticles in bulk films of PSCs requires large concentration to keep interval distance which would increase the chances of recombination of photogenerated electrons and holes,which will induce worse device property.Herein,we demonstrate a significant increase of PCE for PSCs by incorporating the lower concentration of metallic nanoparticles into perovskite/spiro-OMeTAD?HTL?interface.This method is beneficial for the charge separation process,in the mean time,the lower concentration of plasmonic nanoparticles can decrease recombination caused by higher concentration.The main work is divided into the following three parts:?1?Influence of Au NRs@SiO₂ interfacial modification on organic perovskite solar cells:Herein,we demonstrate a significant increase of PCE for PSCs by incorporating high aspect ratio Au nanorods?Au NRs?into perovskite/spiro-OMeTAD interface.To forbide recombination,a thin insulating SiO₂ film is coated around the Au NRs?Au NRs@SiO₂?.The key feature of this approach is that we can take advantage of the SPR at a lower concentration and the Au NRs have larger light scattering section than Au NPs.It is found that the SPR and scattering effect of Au NRs@SiO₂ lead to a broad enhancement of light absorption.Furthermore,a superior enhanced charge separation process in the Au NRs@SiO₂ incorporated device is also observed.Benefitting from this cooperative SPR of Au NRs@SiO₂ in optical and electrical aspects,both short-circuit current density and open-circuit voltage are improved,resulting in the new device delivering a PCE from 14.39%to 17.39%.This result furtherly concludes that Au NRs@SiO₂ has better SPR effect on perovskite/HTL interface,rather than incorporating them into bulk films.?2?Influence of Au-Ag NSs@SiO₂ interfacial modification on inorganic perovskite solar cells:In the previous work,we obtaine that Au NRs can play a more effective SPR effect on perovskite/spiro-OMeTAD interface,rather than incorporating them into bulk films.Perovskite materials are more promising to develop in the inorganic direction because of their instability;the reported inorganic perovskite material?CsPbBrI₂?has excellent thermal stability.Therefore,we select CsPbBrI₂ as absorber layer material to prepare inorganic PSCs.However,in the inorganic CsPbBrI₂ PSCs,the absorption layer film prepared by one-step method has disadvantages of poor crystallinity,thin film thickness,poor absorption of light,and low photocurrent density.We increase the thickness and crystallinity of the absorber layer film by introducing DMSO and anti-solvent chlorobenzene in the precursor solvent.We conclude that the introduction of DMSO into the precursor solvent can increase the concentration of the solution and the thickness of the absorber layer film;the use of anti-solvent chlorobenzene can increase the nucleation rate of the crystal and thus increase the crystallinity of the film.Compared with Au,Ag has stronger SPR,and the rod-like morphology is also limited;we synthesize shuttle-shaped bimetallic?Au-Ag NSs@SiO₂?nanoparticles with a sharp topography to furtherly explore the SPR of plasmonic nanoparticles on inorganic CsPbBrI₂ PSCs.We conclude that the 0.03 wt%of Au-Ag NSs@SiO₂ was incorporated into the optimized inorganic CsPbBrI₂ perovskite solar cell and measured its PCE was 10.15%;compared with the untreated cell,the cell's current density and open circuit voltage have been greatly improved.?3?Influence of Au@CZTS hole transport materials?HTM?on all-inorganic perovskite solar cells:We can learn that the plasmon effect enhances the absorption of incident light and charge separation in perovskite solar cells from the above two experiments.In order to develop an all inorganic perovskite solar cell,we have focused our concentration on synthesizing an inorganic hole transport material which has a dual function of charge transport and light scattering which is different from the conventional hole transport materials.Among the inorganic hole transport materials,Cu₂ZnSnS₄?CZTS?quantum dots have an advantage of better matching with the energy level of perovskite materials and carrier mobility,which are suitable for the fabracation of PSCs.Based on above points,we devote our effort to synthesize Au@CZTS hole transport materials which can enhance the optical and electrical properties of PSCs.The synthesized Au@CZTS hole transport material was deposited on the inorganic CsPbBrI₂ perovskite layer by spin coating,and the PCE of this cell is 6.82%,while the PCE of the cell using CZTS as the hole transport material is only 5.63%.