Improving The Performance Of Perovskite Solar Cells By Adding Additive In The Electron Transport Layer

Recently,solar cells based on halide perovskite absorbers exhibited a very high efficiency.Despite its rapid development,the optimization of film morphology is still a challenging problem,especially in the inverted planar structure.In addition,the modification of the interface between the electrode and the perovskite has become a hot topic.In this paper,we investigated the preparation conditions of perovskite films in inverted planar structure perovskite solar cells,and then additive was added in the electron transport layer to improve the performance of the device.1.The preparation conditions of the perovskite films.During one-step method,we adjusted the precursor concentration,spin speed to decide the optimal concentration and optimal spin speed;Different concentrations of 1-chloronaphthalene additive was added to adjust the morphology of the films to determine the optimum concentration of the additive.For two-step method,by changing the solvent used in the second step,the annealing manner,the annealing time to selecte the solvent,the annealing time and annealing manner.Finally,two-step method was adopted because perovskite film processed by two-step has better morphology,wherein the second step employing isopropanol as a solvent,and then annealing in a hotplate for 20 min.2.Polyethylenimine(PEI)as an additive in the electron transport layer.PEI was added to improve the film-forming property of PCBM on perovskite film without any negative effect on the electron transport property of PCBM.Thus,the leakage current reduced at the interfaces between the perovskite,PCBM films and the top Al electrode.Meanwhile,the electron-rich PEI can improve the performance of the devices by passivating the trap states at the perovskite surface or crystal boundaries which will lead to undesired charge recombination.The best device was obtained when adding 3 wt % PEI,PCE was increased from 3.97 % to 10.72 % compared to the device without PEI,with Voc = 0.95 V,Jsc = 15.95 mA/cm2 and FF = 70.40%.3.Poly(9-vinylcarbazole)(PVK)as an additive in the electron transport layer.PVK can improve the film-forming property of PCBM on perovskite film and decrease the roughness of PCBM when increase the concentration of PVK in a proper extent since PVK can well mixed with PCBM due to the oil-soluble nature.Furthermore,PVK also passivate the trap states at the perovskite surface or crystal boundaries as PVK have N-containing carbazole group.The best device was obtained when adding 4 wt % PVK,a PCE of 9.91% was achieved,where Voc = 0.95 V,Jsc = 15.95 mA/cm2,FF = 65.41 %.