Progress on strategies to control the built-in electric field of perovskite solar cells

Abstract

<p indent="0mm">Perovskite solar cells (PSCs) are high-efficiency and low-cost photovoltaic devices that have been extensively studied by researchers around the world. The carrier separation and transport inside the solar cell is the key process of the device operation, which is directly related to the photoelectric conversion efficiency (PCE) of the device. The built-in electric field formed by the heterojunction dominates the behavior of carriers, and its strength determines the separation efficiency of electrons and holes in the device. Therefore, regulating and optimizing the built-in electric field can fundamentally improve the performance of the solar cells. Much work is focusing on the built-in electric field for the fabrication of high-efficiency devices. According to previous results, this paper firstly introduces some fundamental experiments on the heterojunctions and the mechanism of carrier separation and transport of PSCs. Secondly, the regulation strategies of the built-in electric field commonly used in perovskite solar cells and their effects on device performance are summarized. The following are the most common built-in electric field control strategies: (1) Tuning the built-in electric field of perovskite solar cells by doping. The method of doping to control the built-in electric field is to add appropriate impurities according to different conductive properties of the materials. According to the structure of planar perovskite solar cells, doping the electron transport layer, hole transport layer, and perovskite layer of PSCs with different doping materials can change the position of the Fermi level and further enlarge the splitting of the Fermi level which can assist in the separation and transport of carriers. (2) Tuning the built-in electric field of perovskite cells by constructing 3D/2D perovskite heterojunctions. Fabrication of 3D/2D heterojunctions can not only improve the PCE of perovskite solar cells, but also improve its stability, so this method is more popular among researchers. The construction of 3D/2D perovskite heterojunctions can expand the splitting of the Fermi level to form a more powerful built-in electric field. This method can increase the separation and transport efficiency of carriers, and improve the PCE and open the circuit voltage of the device. (3) Tuning the built-in electric field of perovskite cells by constructing a dipole layer. Electric dipoles have the property of changing the work function of materials. Using them can effectively adjust the energy level structure of perovskite solar cells, expand the work function difference, and increase the built-in electric field strength to achieve the effect of enhancing carrier separation and transport efficiency. The above three methods are relatively popular control strategies for the built-in electric field of perovskite solar cells and this paper systematically analyzes and summarizes them. In the end, we evaluate the built-in electric field regulation technologies of perovskite solar cells, and look forward to the future development of this field. Enhancing the built-in electric field of perovskite solar cells is the key to improving the PCE of the device. In the future, more research should be devoted to the study of the built-in electric field of perovskite solar cells.