High Performance Lead-Based Perovskite Solar Cells Regulated With Organic Alkali Metal Salts

Organic-inorganic halide perovskite solar cells(PSCs)are the fastest developing photovoltaic technology in recent years.Halide perovskite material has the advantages of high light absorption coefficient,wide adjustable band gap range,low exciton binding energy,long carrier diffusion distance,bipolar charge carrier migration and high dielectric constant due to its unique ionic structure.These excellent optical and electrical properties make it show great research value and application prospect in photovoltaic field.In just over ten years,its photoelectric conversion efficiency has increased from 3.8%to more than 25%,almost meeting the efficiency requirements of commercial silicon-based solar cells.However,in the process of commercialization of perovskite solar cells,there are still many challenges and obstacles,including crystal regulation of light absorption layer,interfacial charge transfer,reproducibility of high-performance devices,hysteresis and overall stability of devices,etc.Given the above main problems,researchers put forward a variety of optimization strategies.It is a simple and effective strategy to improve the photoelectric conversion efficiency(PCE)and stability of perovskite solar cells by introducing multifunctional small molecules containing special functional groups to modify the non-ideal defects of perovskite layer or interface layer.In view of this,we introduced small molecule organic alkali metal salts into the light absorption layer and electron transport layer of organic and inorganic perovskite solar cells,and systematically studies the crystallization kinetics of perovskite absorption layer,interface structure of the transport layer,photoelectric conversion performance and stability,etc.The main research contents are as follows:(1)Potassium trifluoromethanesulfonic acid(FSK)doped halide mixed perovskite thin films were prepared by sol-gel spin-coating method.The effects of FSK doping on the crystal morphology,crystallization kinetics,photoelectric properties,band structure and photoelectric conversion efficiency of the perovskite thin films were systematically studied.The results show that the smaller size of K+ can enter into the lattice of perovskite film.causing lattice shrinkage and improving the phase structure stability of perovskite film.Trifluoromethanesulfonate can coordinate with PbI2 to form mesomorphic products,which can delay the crystallization rate,inhibit the precipitation of fine grains at grain boundaries,and promote the orientation growth of(100)and(200)crystal planes.Atom F with strong electronegativity can form hydrogen bond with FA+/MA+ to inhibit the thermal decomposition of cation in bulk phase and improve the thermal stability of perovskite film.Compared with the undoped perovskite film,the intrinsic band gap of FSK-doped perovskite film does not change significantly,but the position of the perovskite film conduction band decreases by 0.09 eV through UPS characterization,showing a level structure that is more consistent with SnO2.The lower electron transition extraction barrier improves the carrier transport efficiency at the interface.At the same time,electron-hole quenching of the perovskite film was alleviated,showing stronger PL strength and an ultra-long charge carrier lifetime(5049 ns).FSK-based perovskite solar cell devices have lower defect density,higher composite resistance and lower interfacial composite energy loss.After device optimization and morphology comparison,the optimal FSK doping amount is determined to be 1 mg/mL.A solar cell test device was assembled using tin dioxide as the formal structure of electron transport layer,and the photoelectric conversion performance and stability of the assembled device were tested using IPCE and sunlight simulation system.Finally,the optimal PCE of 20.37%was obtained by combining organic multifunctional molecules with alkali metal cationic co-doping.After aging in air for 600 h,the device still retains more than 77%of the PCE and 63%of the PCE under continuous light.(2)In order to solve the aggregation phenomenon of SnO2 nanoparticles in colloidal solution,potassium citrate(PCA)was introduced into the SnO2 electron transport layer film as a SnO2 particle modification additive.The effects of PCA on the morphology,interface contact,band structure,carrier transport kinetics and photoelectric conversion capability of the device were investigated.The results show that the introduction of PCA can inhibit the hydrolysis of SnO2 colloid,weaken the van der Waals forces between nanoparticles,and contribute to the orderly arrangement of nanoparticles,thus achieving the formation of high-quality SnO2 electron transport layer films.The interaction between PCA and SnO2 nanoparticles was characterized by infrared spectroscopy and X-ray electron spectroscopy.Abundent carboxyl group in citrate ions can effectively complex with Sn4+,reducing the adsorption between metal oxide particles.Compared with undoped SnO2 films,PCA-doped SnO2 films showed higher conductivity,better morphology and better surface roughness(RMS reduced to 1.49 nm).At the same time,the rich carboxyl and hydroxyl groups at the interface can establish chemical connections with perovskite through lone pair electron coordination complexation and hydrogen bonding,improve the interface contact of perovskite and regulate the crystallization kinetics of perovskite.Through transient photocurrent,voltage and electrochemical workstation tests,the influence of PCA on carrier transport dynamics was revealed.It was found that the carrier recombination efficiency in the device was reduced and the interface showed better contact selectivity.At room temperature,the PCA-doped SnO2 planar perovskite solar cells assembled based on room temperature perovskite preparation technology have the highest filling factor of 79.10%,the open-circuit voltage of 1.145 V,and the best efficiency of 21.25%.In addition,the stability of PCA-modified cell devices was also improved.The unpackaged devices maintained an initial efficiency of 90%after 1000 h storage in ambient air,85%after 500 h aging at 85℃,and 66%after 500 h exposure to sunlight.