Preparation And Optimization Of Perovskite Solar Cells Based On CH₃NH₃PbI_3-xCl_x

In recent years, solar cells have been developed quickly, and the new types of solar cell materials, structures and techniques have emerged in an endless stream. Perovskite solar cell is the best, compared with other new solar cells. This solar cell has a series of advantages, such as the wealth source of preparing materials, the low cost, the simple production process and environment friendly. The most important thing is that it has the highest power conversion efficiency?PCE? among the third generation solar cells. At present, the efficiency up to 20% has been achieved.The perovskite solar cells we prepared have the conventional mesoporous structure. the solar cell exhibits the typical sandwich structure, from the bottom to the top, FTO conductive glass /TiO₂ compact layer?barrier layer? /TiO₂ electron transport layer?mesporous layer? / absorbed layer/hole transport layer/Au electrode. As a core part of the solar cell, the common light-absorbed materials include CH₃NH₃PbI_3-xCl_x, CH₃NH₃PbI₃, CH₃NH₃PbI₂Br and HC?NH₂?₂PbI. The process of preparing the perovskite layer includes one-step spin-coating method, two-step method and double source co-evaporation. The hole transport materials are divided into organic materials and inorganic materials, for the former, Spiro-OMe TAD and Poly?3-hexylthiophène??P3HT? are the representatives. The latter refers mainly to CuI and CuSCN. The object of study in this thesis is the perovskite solar cells which are based on CH₃NH₃PbI_3-xCl_x materials, and we focus on how to optimize the manufacturing processes and conditions of the electron transport layer, the perovskite layer and the hole transport layer to improve the performance of the solar cells. In the process of assembling solar cells, we adopt some preparation method, for example, the TiO₂ compact layer is prepared by soaking FTO conductive glass in the TiCl₄ aqueous solution. TiO₂ electron transport layer is prepared with hydro-thermal method. Spin-coating method is used to prepare the perovskite absorbing layer and hole transport layer. The Au electrode is deposited with the thermal evaporation method.This thesis mainly includes the following three sections:In chapter two, we studied the effect of the two additives different concentration of bis?trifluoromethane? sulfonimide lithium salt?Li-TFSI? and 4-tert-butylpyridine?D-TBP? in P3HT/ solution on the hole transport layer and the performance of the solar cell. Before spin coating the solution, different quantity of Li-TFSI?dissolved in acetonitrile, 520mg/mL? and D-TBP are added to four bottles of 1mL P3HT/ solution, respectively 0?L and 0? L, 18?L and 20?L, 36?L and 38?L, 72? Land 74?L. Four different P3HT layers and solar cells are prepared, labeled as P0, P1, P2 and P3. SEM topview images of P3HT hole transport layers display that the coverage rate of P3HT film increases obviously and the gap of the layer decreases apparently with the increase of the concentration of the additives. Hall effect measurements data show that the hole mobility increases first and then decreases with the increase of additives concentration. Simulation parameters of Electrochemical Impedance Spectroscopy of the solar cells reveal that the solar cell has the minimum charge transport resistance when the additives concentration is the best. Finally, the best solar cell gets the efficiency of 9.7%, increasing by 90%, compared with the reference solar cell?additives are not added in the P3HT solution? under the AM1.5G.In chapter three, we investigated the influence of hydrothermal temperature on TiO₂ electron transport layer and the performance of the perovskite solar cell. We prepared TiO₂ electron transport layer at 140 and 170? and? assembled CH₃NH₃PbI_3-xCl_x solar cells based on the TiO₂ layers. XRD patterns of TiO₂ show that both of them are rutile structure, but the TiO₂ layer prepared at 170 has a stronger peak.?SEM images of the cross-sections reveal that the latter crystal is one-dimensional nanorod arrays, These nanorods are ordered closely and densely. In a word, the former has not obvious geometry shapes, and there are apparent gaps in the crystal. The simulation parameters of Time-Resolved Photoluminescene Spectra?TRPL? and Electrochemical Impedance Spectroscopy?EIS? indicates that compared the TiO₂ crystals prepared at 140?and 170?, the electron has a longer life and smaller value of transport resistance in latter. The efficiency of solar cells using the TiO₂ crystal films prepared at 140? and 170 as the HTM?layers is 9.1% and 13.8%, respectively. The efficiency of the latter is increased by 51% compared with the former. After 7 days kept in the air, the efficiency of two solar cell smaples is reduced to about 73% of the initial values.In chapter four, the performance of perovskite solar cells is improved by optimizing the CH₃NH₃I synthetic condition, annealing temperature and time of the perovskite absorbing layer. We set up three different volume ratio, 10.23mL: 10mL, 9.3mL: 10mL and 8.37mL: 10mL, when using CH₃NH₂ and HI to synthesis CH₃NH₃I. We prepare the perovskite solar cells with the synthetic CH₃NH₃ I. The J-V characteristic curves of the solar cells are obtained under 100mW/cm2, showing that the solar cell gets the efficiency of 14.4% using the CH₃NH₃ I which is synthesized according to 9.3mL: 10mL?CH₃NH₂ :HI?. It should be pointed out that its open circuit value is 1.05V with P3HT HTM. Such a high voltage is very rare. In order to find out the optimal annealing temperature and time of the perovskite layer, we set up respectively three kinds of annealing temperature 120?, 110?, 100? and annealing time: 30min, 45min, 60min. Under 100mW/cm² sun illuminations, we get the J-V characteristic curves of 6 kinds of solar cells. When the annealing temperature and time are respectively 110 and 45? min, the short circuit current density, open circuit voltage, filling factor and power conversion efficiency of the device all achieve maximum values. They are 27.2 mA/cm², 0.996 V, 64.2% and 17.4%, respectively. The efficiency of best solar cell is increased by ³5% compared with the reference device?120 and 30? min?. The simulation parameters of Electrochemical Impedance Spectroscopy?EIS? reveal that the best device has the maximum charge recombination resistance value of 113.4?cm² and the constant phase element parameter CPE-P value of 0.78, and the minimum charge transport resistance value of 385?cm² after the optimizing the annealing temperature and time of perovskite layer.In chapter five, summary of scientific research during my graduate period and prospect of future research are given.