| Flexible perovskite solar cells（F-PSCs）are excellent new flexible electronic devices with high power conversion efficiency（PCE）and good flexibility.With the increasing demand for flexible electronic devices,F-PSCs have broad development prospects and gradually becoming a research hotspot in the field of new generation flexible electronic devices.However,in practical applications,F-PSCs are prone to irreversible damage to their various functional layers when subjected to external mechanical loads,seriously affecting the bending stability of the device.To solve this problem,the structure and performance of the battery from the perspective of bending mechanics have been analyzed,and the stress distribution and deformation of the device and its various functional layers under different bending radius through finite element simulation have been studied.At the same time,the effects of bending stress on the morphology,structure and performance of indium tin oxide（ITO）and perovskite（PVK）films through experimental research have been studied,and the bending stability of F-PSCs at room temperature and high temperature have been discussed.The main research contents of this article are as follows:（1）The various functional layers of the flexible perovskite solar cells were prepared by spin-coating process,and the load-displacement curves of each functional layer were measured by nanoindentation method.The elastic modulus of ITO film,tin oxide（Sn O2）electron transport layer,PVK film,hole transport layer（Spiro-OMe TAD）film and silver top electrode（Ag）film were calculated to be 23.04,24.00,14.56,9.46and 10.06 GPa,respectively,and the hardness values were 5.50,4.70,0.77,0.18 and0.31 GPa,respectively.（2）According to the geometric structure of the flexible perovskite solar cells,we drew its two-dimensional geometric model with finite element software,and simplified the model reasonably.The length of the model was set to 119μm,the thickness was5.95μm,and the virtual width was 89.25μm.Before the loading calculation,the model was meshed.After comparing the existing model with the refined model,the error was only 0.0312%,which verified the reliability of the model.Then,by setting different boundary conditions to simulate the different stresses experienced by F-PSCs,it was found that as the bending radius decreased from 5 mm to 1 mm,the maximum stress value of the device increased from 4181.7 MPa to 15763.9 MPa,and the maximum displacement increased from 0.020 mm to 0.047 mm.Meanwhile,the stress and displacement variations of ITO films and perovskite films have been investigated.When the bending radius was the same,the stress value of ITO film was greater than that of perovskite film,but the displacement changes of the two was the same,with the maximum displacement change in the central region of the model decreasing gradually to both sides.In addition,the effect of temperature on the bending mechanical properties of F-PSCs was investigated,and the bending under the same bending radius（5,3 and 1 mm）at high temperature（80℃）and room temperature was simulated and compared.The maximum stress value and maximum displacement value of F-PSCs at80℃were larger than those at room temperature,indicating that the bending stability of F-PSCs at high temperature may be lower than that at room temperature under the same bending radius.（3）To further study the bending stability of F-PSCs,we set different bending radius（5,3 and 1 mm）to bend each 10 times to represent different stresses.When the bending radius decreased from the initial state to 1 mm,the crack density on the surface of the ITO film gradually increased,and there was peeling phenomenon,and the surface roughness increased from 4.89 nm before bending to 18.60 nm.At the same time,the square resistance of the ITO film increased significantly.When the bending radius decreased,the crack density on the surface of the perovskite film also increased gradually,but there was no peeling phenomenon.Besides,it may be related to the fact that it bears a smaller stress compared with the ITO film,consistent with the simulation results.The half-peak width of the（110）diffraction peak of the perovskite film increased from 0.164 before bending to 0.236,and the water contact angle decreased from 67.8°to 40.7°,indicating that the surface structure of the perovskite film was destroyed and the quality gradually deteriorated as the bending radius decreased.Subsequent analysis of the photoelectric properties of the perovskite film showed that the initial optical bandgap of the perovskite film was 2.06 e V.The optical band gap increases to 2.16,2.21,and 2.29 e V after bending at bending radii of 5,3,and 1 mm,respectively.This indicates that excited electrons are difficult to be excited to the conduction band,which leads to recombination within the perovskite film and reduces the performance of the perovskite film,and the average decay lifetime of carriers in the perovskite film decreases from 20.44 ns to 18.71 ns.Finally,the bending stability of F-PSCs at different bending radius and temperatures was discussed.When the number of bends reached 100 times at room temperature,the PCE of F-PSCs with bending radius of 5,3,and 1 mm decreased by about 25%,37.9%,and 41.2%,respectively.Under the same bending radius and number,the efficiency at 80℃decreased by about 44.3%,58.2%,and 67.1%.The results showed that high temperature would have a negative impact on the bending stability of F-PSCs. |
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