| As we all know, solar energy is a kind of renewable and clean energy, which can be converted into electrical energy by solar cells. As one of the most popular third-generation solar cells, the perovskite solar cell is based on inorganic-organic metal halide material, which is as the layer of light absorbers, photoelectric conversion and photogenerated carrier transport. Perovskite materials with adjustable optical bandgap(1.48-2.3e V) and high absorption coefficient(more than 104 cm-1) can absorb the light below 800 nm with only a few hundred nanometers in thickness. Meanwhile, the perovskite solar cells allow significantly reducing the cost in comparison to other solar cells by means of using all solution-processed techniques. Therefore, the perovskite solar cells have a promising prospect.The chemical formula of perovskite materials is ABX3. CH3NH3 Pb I3 is one of the most commonly used among various perovskites, where CH3NH3+ is the A, Pb2+ is the B and I- is the X. However, the progress of the commercialization of the perovskite solar cells has been hindered due to the instability of the current used perovskite materials. Therefore, in view of the stability of the perovskite structure, we aimed to use other elements to replace or partially replace the A and X so that we can get the new perovskites solar cells with high structural stability. There are many elements that can replace the CH3NH3+, such as HC(NH2)2+, Cs+ and so on. We used HC(NH2)2+ to replace part of CH3NH3+ to get compact perovskite layer with higher lattice energy.We also doped metal ions into perovskite materials to increase the coverage. Meanwhile, we employed Cl and Br to partially replace the I so as to eliminate the uncoordinated iodine ions located at the surface of perovskite thin film. On the basis of obtained perovskite thin film with high density, high coverage and high stability, we prepared efficient perovskite solar cells. This article investigated the performance of perovskite thin films and perovskite solar cells through a variety of testing methods. Such as X-ray Diffraction(XRD), UV-visible light absorption(Abs), Scanning Electron Microscopy(SEM), X-ray Photoelectron Spectroscopy(XPS), I-V, external quantum efficiency(EQE) and other methods. The main results obtained are as follows:Firstly, we prepared the precursor materials CH3NH3X(X= Cl, Br, I)(referred to MAX) and HC(NH2)2I(abbreviated FAI) which are necessary to synthesize perovskite thin films. XRD results showed that we have successfully prepared the pure MAX and FAI powders.Secondly, we prepared the perovskite thin films by means of components engineering in view of structural stability, by which, the elements located at the positions of A or X were replaced/practically substituted.(i) Changing the X: we prepared three kinds of perovskite thin films which are pure I, I mixed with Cl, and I, Cl mixed with Br.(ii) Changing the A: doping metal ions inside perovskite thin film on the basis of Cl-doped and using FA+ to replace part of MA+. We utilized XRD, Abs and SEM to probe the prepared perovskite films with different structures and the results showed that the structure and morphology of perovskite thin films can be effectively mediated, the corresponding photovoltaic performances, including hysteresis, photocurrent, conversion efficiency have been significantly improved by changing A and X in perovskite.Finally, we fabricated perovskite solar cells using the prepared perovskite thin films with different structure. And we optimized the perovskite solar cells based on the optimal perovskite thin film prepared by I mixed with Cl via one-step method. The perovskite solar cell with photoelectric conversion efficiency of 13.6% has been consequently reached without hysteresis by adjusting the parameters. |
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