| The perovskite solar cells using CH3NH3PbI3 thin film as absorption layer, have the advantages of simple preparation process, low temperature of preparation, low cost and high efficiency, compared to the conventional solar cells. Since 2009, the technology of perovskite solar cells have maintained good momentum of development, and the corresponding photoelectric conversion efficiency increased from 3.8% to 20%. Perovskite materials with CH3NH3 Pb I3 structure are direct band gap semiconductors, which have evident advantage in high light absorption, wide absorption spectrum, low exciton binding energy, high carrier mobility and long carrier diffusion length. CH3NH3 Pb I3 can directly absorb photonics and convert them into photogenerated carriers, and then transfer them. As a consequence, the CH3NH3 Pb I3 can be used for an efficient light absorbing layer of p-i-n type planar heterojunction solar cells. The CH3NH3 Pb I3 can facilely be synthesized by chemical reaction between CH3NH3 I and Pb I2, where both materials are easily synthesized and available. Then, CH3NH3 Pb I3 materials are beneficial to reduce the preparation cost. By using the optimal solven type, spin coating and annealing process, we can remarkably improve the morphology of perovskite films to enhance the open circuit voltage, filling factor and photoelectric conversion efficiency. Based on the above advantages, perovskite solar cells are expected to become a new generation of solar cells with high performances.The dissertation focus on the preparation technology of perovskite solar cells by one-step method, and its main contents contain two part:(1) The study on sec-butyl alcohol assisted preparation technology;(2) The study on the efficiency improvement by using concaveconvex PEDOT:PSS surface. In the conventional thin film preparation of perovskite solar cells by one-step solution process, it is very difficult to control the crystallization and morphology of the perovskite thin films due to the high boiling points of DMF solvent(153 ℃) and the different dissolubility of the CH3NH3 I and Pb I2 in DMF. Then, a typical film surface has a poor morphology, where a large number of pin-hole defects exist. To solve the problem, in the present experiment, we overdose CH3NH3 I in the preparing process of perovskite solution to increase the dissolubility of Pb I2 in DMF. In the process of spin coating of perovskite solutions, we drop some sec-butyl alcohol to promote the fast crystallization of the perovskite, and form flat and uniform perovskite thin film. Finally, the excess CH3NH3 I can be removed through the soaking process by sec-butyl alcohol. This sec-butyl alcohol assisted one-step solution method can effectively control the crystallization and morphology of the perovskite films. By optimizing the washing time, the amount of washing and the soaking time of sec-butyl alcohol, we fabricated a standard solar device with an efficiency of 15.45%. To further improve the efficiency based on the standard device technology, we incorporate polystyrene microspheres with a certain volume ratio into PEDOT:PSS surface, and then use chloroform to remove these polystyrene microspheres, to produce concaveconvex structures in the surface of the PEDOT:PSS. The concave and convex structures in the PEDOT:PSS surface can scatter the incident light, prolong the propagation path of the incident light in the perovskite active layer(i.e., increase the optical path), and then make the light absorption of the perovskite layer stronger. With the contact area between PEDOT:PSS layer and perovskite layer increases, the transporting capacity of holes can be improved. Experimental results show that the concave-convex structures can effectively enhance both the short circuit current density and the open circuit voltage, and the final efficiency of the optimal device can be up to 16.92%. |
