High-Efficiency And Stable Cesium-Lead-Based All Inorganic Perovskite Solar Cells

In recent years,Perovskite solar cells（PSCs）have made great progress in certified photoelectric conversion efficiency（PCE）（from 3.8% in 2009 to the current25.2%）,which is mainly owing to its excellent photoelectric properties such as adjustable energy band-gap,low defect density and high carrier mobility.Meanwhile,the merits of the low cost and simple solution-processed fabrication also make perovskite solar cells a huge commercial prospect.However,the further commercialization of PSCs is constrained by the problem of unstable thermal stress of organic-inorganic hybrid perovskite materials,thus solving thermal stability has become a key technical bottleneck.Cesium-lead-based all-inorganic perovskite solar cells have received widespread attention and have become one of the breakthroughs in solving photo-thermal stability.They have a suitable band gap（1.73-2.3 e V）,which can fulfill the requirement to be a perfect tandem partner,such as crystalline silicon cells,CIGS cells,and narrow band gap perovskite cells,which helps to break the efficiency limit of solar cells.Unfortunately,the black phase of inorganic perovskite face the challenges of the thermodynamic phase transition.Its photo-sensitive black phase（α,β,γ phase）is unstable especially in humid environment,which will spontaneously phase-transition to the non-perovskite structure yellow phase（orthogonal δ phase）.In addition,though the all-inorganic perovskite solar cells have made significant progress,their PCE is still far behind the organic-inorganic hybrid perovskite solar cells.In view of the above scientific and technical problems,this paper systematically studied the black γ phase of the cesium lead-based halide inorganic perovskite CsPbI3-x Brx,stabilized the γ-CsPbI3-xBrx black phase in three different ways.At the same time,through additives engineering,component optimization,interface energy band adjustment and surface passivation,the final optimized cesium-lead-based all-inorganic perovskite solar cell obtained more than 20% of PCE,which is at the leading level among similar cells.Meanwhile,the storage and light stability of the device have also been systematically studied.The main research results obtained in this paper are as follows:1)It is proposed to introduce the organic salt phenethylammonium iodide（PEAI）to stabilize the γ-CsPbI3 black phase and form two-dimensional（2D）perovskite to passivate perovskite defects,which significantly optimizes the Voc and PCE of CsPbI3 solar cells.We use the organic salt PEAI to stabilize the black phase of the inorganic perovskite CsPbI3 and regulate the excessive lead acetate content to control the composition of the two-dimensional perovskite PEA2 Pb I4 in the perovskite,play a role in passivating CsPbI3.We have prepared a planar structure all-inorganic perovskite solar cell with a PCE of 17%,and obtained the highest open circuit voltage of 1.33 V and the smallest Voc loss of 0.38 V among the inorganic perovskite CsPbI3.At the same time,we also studied the humidity stability of this perovskite solar cell.After being aged in dry air for more than 2000 h,the device efficiency only dropped by 6.1%.2)Use the perovskite precursor（HPbI₃）instead of lead iodide（Pb I2）to add into the CsPbI3-x Brx perovskite,which can stabilize the γ-CsPbI3-xBrx black phase under low-temperature annealing conditions.At the same time,through regulating the transport layer interface,a cesium-based perovskite solar cell with a PCE of more than 18% was prepared.We applied lithium fluoride（Li F）as Interface buffer layer which can reduce the work-function of Sn O2 layer,making the better energy level alignment and also can passivate the interface defect.In addition,by incorporating lead chloride（Pb Cl2）in CsPbI3-x Brx precursor,the perovskite film crystallinity is significantly enhanced and the charge recombination in perovksite is suppressed.As a result,optimized CsPbI3-x Brx PSC exhibits excellent performance with the VOC as high as 1.25 V and an PCE of 18.64%.Meanwhile,a superior photo-stability with a less than 6% efficiency drop is achieved for CsPbI3-x Brx PSCs under continuous 1 sun equivalent illumination over 1000 h.3)Using component control engineering and surface passivation engineering,an all-inorganic perovskite solar cell with a PCE of more than 20% has been developed.On the Sn O2/Li F substrate,we use component engineering to precisely control the ratio of HPb I3 to Pb Br2 to obtain the perovskite film with better quality.As a result,a PCE=19.2%,Voc=1.315 V CsPbI3-x Brx all-inorganic solar cells was achieved.In addition,the organic salt DMAI is applied as an additive to stabilize the γ-CsPbI3-xBrx black phase,regulating the Cs F concentration of the surface passivation and combining with Li F to prepare a Li F/perovskite/Cs F double-sided modified layer,finally,the device has a PCE of more than 20%.In conclusion,we have systematically studied the thermodynamically stable orthorhombic phase with suitable band-gap（γ-CsPbI3-xBrx）,and we stabilized γ-CsPbI3-xBrx by incorporating organic salt PEAI,precursor HPb I3,and organic salt DMAI.Furthermore,the additive engineering,component optimization,interface band adjustment and surface passivation were used to prepare a high-efficient and stable all-inorganic perovskite solar cell with PCE of more than 20% and excellent light stability performance.This highly efficient CsPbI3-x Brx can promote basic research on all-inorganic perovskites and their potential applications in optoelectronic devices.