Effect Of Novel Perovskite Additives On The Performance Of Their Photovoltaic Devices

Solar energy,which is inexhaustible,is a very clean energy source.Solar cells are the main devices for converting solar energy into electrical energy.Perovskite solar cells（PSCs）are the focus of current research.After a decade of development,the efficiency of perovskite solar cells has been exceeded 24%.The bottlenecks of perovskite solar cells are the stability issues.Perovskite is sensitive to water,oxygen,heat,light,etc.,which can cause perovskite decomposition.Two main aspects determine the stability of PSCs:Firstly,the intrinsic unstable properties of perovskite.Secondly,interface issues.This thesis focuses on these two aspects,applying additive method to improve the stability of the perovskite material and using double-layer interface method to develop the stability of PSCs.As follows:（1）Mixed halide PSCs(CH₃NH₃PbI_3-x-x Cl_x)are prepared by adding a novel chlorine containing additive,chloroformamide（Cl-FACl）.Efficiency and stability are obviously improved by incorporating with Cl-FACl compared with CH₃NH₃PbI₃.Mixed halide perovskite has excellent optoelectronic properties and benign device stability.However,Cl doping is difficult to obtain due to gas MACl.Cl-FACl has a higher boiling point and is more difficult to volatile than MAC1.The champion device with Cl-FACl shows a efficiency up to 20.36%,while the control device is18.9%.In addition,device with Cl-FACl maintains 94%of its initial efficiency after MPP test（AM1.5G）for ten hours,while the control devices degrade more than 50%in 100 minutes.Therefore,efficient and stable mixed haldie PSCs can be obtained by incorporated with the novel Cl containing additive.（2）Highly efficient and stable PSCs are fabircated by incorporation of high boiling point methyl sulfoxide group（S=O）containing additives.A tiny of DMSO residual has been demonstrated in the as prepared perovskite films.During the illumination,the PSC is simultaneously affected by light and heat,and the residual DMSO in the film is slowly evaporated,new defects are thus generated inside the film.In order to suppress the these defects caused by the volatilization of DMSO,high boiling point additives containing a sulfoxide group are introduced into the device,including methyl methylsulfinylmethyl sulfide（MMTS）,dibutylsulphoxide（DBSO）,（methylsulfinyl）benzene（MPSO）,Diphenyl sulfoxide（DPSO）,so that they can maintain the passivation under the effect of light and heat.The XPS results demonstrate stronger interaction with Pb for these high boiling point additives than DMSO.The introduction of dopants makes the PSCs have both high efficiency and better device stability.Among these additives,PSC doped with MMTS presents efficiency up to 19%and maintains about 90%of its initial efficiency after MPP test（AM1.5G,without UV filter）for more than 2000 minutes,while the control device degrades more than 50%in 100 minutes.It illustrates that the addition of high boiling point additives containing sulfoxide groups can effectively improve the stability of the device and also provides a new idea for the selection of additives.（3）High-efficiency and stability PSCs are prepared by replacing DMSO with liquid zirconium acetate（Zr（Ac）₄）as an additive to assist the film formation of perovskite with N,N-dimethylformamide（DMF）as single solvent.The incorporation of DMSO has negative effect on the stability of PSCs.Device prepared with pure DMF has better stability,but the efficiency is very low.In order to obtain high performance PSCs,liquid Zr（Ac）₄ is introduced into the DMF for device fabrication.Alleviation of microstrain inside the perovskite film has been found with the introduction of Zr（Ac）₄.XPS results demonstrate the interactin between I and Zr ions.The film with dopant becomes a more N-type nature resulting in the increase in V_oc.A high PCE of 20.9%is achieved for a PSC with an optimized concentration of Zr（Ac）₄.More than 98%of the initial performance is remained after continuous MPP output testing for 1700 minutes under AM1.5G（without UV filter）for device with Zr（Ac）₄and the device presents almost no decline after successive thermal heating at 90 ^oC for one month.（4）P3CT is used to modified NiO,thermal stability of PSCs besed the modified NiO are largely enhanced.Among the current inverted perovskite solar cells,NiO is the most commonly used inorganic hole transport material,while the thermal stability is extremely poor.Because that P3CT can effectively block the reaction between NiO and perovskite when the device is thermal heated.The efficiency of PSC based on the modified NiO remains 95%after heating at 85°C for 150 hours,while for device without modification,the efficiency decreased to be zero after heating for 60 hours,indicating the obvious modification of P3CT to NiO.