Back Contact Interface Engineering Of Inverted Planar Organic-inorganic Hybrid Perovskite Solar Cells

Recently,organic-inorganic hybrid perovskites are widely used in active layers of solar cells because of their high carrier mobility,direct bandgap,high light absorption and small exciton binding energy,etc.There are two kinds of planar device structures in perovskite solar cells:n-i-p structure and p-i-n structure.Compared with the n-i-p structure,the p-i-n device has drawn more and more attention mainly due to the low hysteresis effect and solution processability.Among the p-i-n perovskite solar cells,the devices employing the nickel oxides(NiOx)as hole-transport layers and phenyl-C61-butyric acid methyl ester PC61BM(or phenyl-C71-butyric acid methyl ester,PC71BM)as electron-transport layers have become research hotspots owing to the low cost and low-temperature processability.However,the efficiency of p-i-n inverted planar perovskite solar cells is low,which is mainly due to the inferior transport of electrons and holes at the device interfaces.There are two important interfaces in p-i-n inverted planar perovskite solar cells:front contact interface(hole-transport layer/perovsite active layer)and back contact interface(perovskite active layer/electron t:ransport layer).So far,many efforts have been devoted to improving the front contact interfaces(hole-transport layers/perovskite active layers).On the contrary,few research work focuses on the back contact interfaces.Actually,the back contact interface is indispensable for high-performance devices.In this work,back contact interface engineering is applied to improve the efficiency and stability of p-i-n inverted planar perovskite solar cells.By inserting a molecular interface layer between the perovskite active layer and PC61BM electron-transport layer,the perovskite solar cells with high efficiency and improved stability are obtained.The main work of this research is summarized as follows:Firstly,the tetrafluoroterephthalic acide(TFTPA)molecular layer is inserted between the perovskite active layer and the PC61BM layer.Then,the coulomb force between the positively-charged benzene ring center in the TFTPA molecules and the electronegative fullerene,as well as the coordination between the-COOH group of TFTPA and Pb"+on the perovskite surface,is used to form a tightly-connected and defect-passivation pero vskite/PC61 BM interface.The formed interface can significantly promote electron transport while reducing charge recombination and accumulation at the perovskite/PC61BM interface.The photovoltaic performance of perovskite solar cells based on TFTPA molecular modification has been significantly improved,with its photoelectric conversion efficiency reaching 19.39%.By contrast,the device without TFTPA molecular modification has a power conversion efficiency of only 16.10%.In addition,the device with TFTPA modification exhibits better air stability.Secondly,the synthesized GuaBF4 molecules are coated on the surface of the perovskite films by spin coating,and the dual ion passivation effect is used to improve the photovoltaic performance of the perovskite film.Gua+can replace the A-site cation in perovskites,and assist the crystal growth of perovskites.In addition,BF4-can effectively passivate the defects at the grain boundaries of the perovskite films.For the perovskite solar cell modified with GuaBF4,a power conversion efficiency of 19.8%is obtained.Besides,the device stability is also improved.In this work,back contact interface engineering is applied to improve the efficiency and stability of p-i-n inverted planar perovskite solar cells,it is a new approach for high-performance inverted planar PSCs.