Research On High-efficiency And High-stability Perovskite Solar Cells Prepared By The Fumigation Method

Organic-inorganic hybrid halide perovskites have attracted a great deal of attention due to their large absorption coefficient,adjustable direct band gap,high charge mobility,abundant material resources,and so on.The power conversion efficiency(PCE)of the perovskite solar cells has been increased from 3.8%to 22.7%since its first report in 2009.However,stability remains to be the main hurdle for its commercialization.Therefore,in this work,we developed a new synthesis technique for the perovskite layer,exploited novel 2D perovskite materials,and designed the structure of perovskite absorber to improve the solar cell efficiency and device stability.The main results are as follows:(1)We developed a dual-source co-evaporation deposition method to fabricate pin-hole-free MAi-xCsxPbI3 perovskite films with complete surface coverage.It is found that the band gap of the perovskite film can be fine-tuned in the range of 1.605-1.651 eV by adjusting the Cs content.The PCE of the device based on MA0.77Cs0.23PbI3 reaches to as high as 20.13%.The perovskite solar cells prepared by this method not only show the high efficiency,but also exhibit significantly higher stability.After being stored in dark for one year,the PCE of the Cs-substituted perovskite solar cells remains at 19.25%with short circuit-current density(Jsc)= 23.38 mA cm-2,open circuit-voltage(Voc)= 1.09 V,fill factor(FF)= 0.75,degraded by only 4.37%of its initial efficiency.(2)We have developed a new strategy to fabricate the 2D perovskite thin films using 2D PbI2 template with high degree of crystallization and preferred orientation.In this 2D perovskite material,the shorter chain MA+ molecules were introduced,and combined with the 2D PbI2 template through vapor permeation.Thanks to the PbI2 template,the 2D MA-based perovskite films were induced to grow along the vertical direction to form films out-of-plane with respect to the substrate.The x-ray diffraction(XRD)and scanning electron microscopy(SEM)results,as well as grazing incidence wide-angle x-ray scattering(GIWAXS)tests demonstrate successful formation of high quality 2D MA-based perovskite films by the new template-mediated vapor-permeation technology.Because of these advantages,including the out-of-plane orientation for effective charge transport,narrow band gap,low trap density,and strong resistance to moisture,the champion device based on the new 2D perovskite yielded a PCE up to 16.95%(the certified PCE at 16.70%)with reduced hysteresis,the highest value among the 2D devices reported.More importantly,the device stability is impressively improved compared with that of their 3D counterparts.The unencapsulated 2D MA-based perovskite solar cell retained 96.6%of their initial efficiency after being stored at ambient with?55%relative humidity for 210 days.(3)We also explored a new technology to shrink grain boundary using long alkyl chain additives through a simple one-step spin-coating process.In this approach,a 'plate-like' perovskite crystallites diffused into the grain boundaries(GBs)of the Cs-doped formamidinium lead triiodide(FA0.95Cs0.05PbI3).We propose an additive engineering strategy using a long alkyl chain additive of phenethylammonium iodide(PEAI)to further modify the film morphology for improved crystalline quality.The high crystallinity and improved structure of perovskite are found to synergistically enhance the PCE and stability of the perovskite solar cells.By introducing PEAI into the simple and widely used FA0.95Cs0.05PbI3,a champion device efficiency of 20.52%is achieved.More remarkably,the high-performing devices can remain over 80%of its initial PCE after 200 h of 85%humidity at 30?;meanwhile,the device also kept over 80%of the initial PCE when aged at 100 ? for 500 h.To our knowledge,both the humidity and thermal stability of perovskite photovoltaic are the best so far.