The grain boundaries and crystal surfaces of polycrystalline thin films have inclusion high-density charge traps, which consequently result in the high resistance of perovskite thin films. To change this electronic property, doping technology is widely used in semiconductor-based photovoltaic devices, especially for silicon and CIGS solar cells ( Gao et al., 2011 Zhu et al., 2012 Jena et al., 2019). Many traditional semiconductor materials, like silicon, indium phosphide, and gallium nitride, have achieved controlled bipolar doping of both N type and P type ( Wan et al., 2018 Yamada et al., 2019). For example, doping can control the physical properties of almost all modern semiconductors, which is also the premise used to realize their industrial applications. However, the level of understanding of these basic semiconductor physics is far below the device fabrication process. However, perovskite semiconductors have many basic physical properties that are sensitive to the intrinsic defects of the material and to intentional doping, such as bipolar doping, carrier transfer characteristic, etc. Over the past few years, MAPbI 3-based perovskite solar cells (PSCs) have made great progress with a current certificated efficiency of 25.2% (NREL). Perovskite materials are widely used for photovoltaics, lasers, photodetectors, light-emitting diodes (LEDs), and thin film transistors ( Dai et al., 2014 Dou et al., 2014 Rajagopal et al., 2018 Schulz, 2018). Perovskite structure has a common ABX 3 configuration, where A is a monovalent organic or inorganic cation like methylammonium (MA +), formamidinium (FA +), or Cs + B is a divalent metal ion like Pb 2+, Sn 2+, or Ge 2+ and X is a monovalent anion like Cl −, Br −, I −, or SCN − ( Beal et al., 2016). Organic–inorganic hybrid halide perovskites have attracted considerable attention in the photoelectric field, due to their low growth cost, long carrier lifetime, low exciton binding energy, and tunable band gap ( Xing et al., 2013 Dong et al., 2015 Brenner et al., 2016 Bai et al., 2018 Jena et al., 2019). These results suggest that sodium doping is an effective way to grow highly conductive p-type MAPbI 3 perovskites. Obvious fingerprints of Na-related acceptor (A 0X) levels in the doped MAPbI 3: Na were observed at 10 K. The optical fingerprints of the doped levels in MAPbI 3: Na perovskites can be identified by temperature-dependent PL. The room-temperature photoluminescence (PL) peaks of doped MAPbI 3 films slightly blue shift, while the photocarriers' lifetime becomes longer. Hall effect results demonstrate that both the MAPbI 3: Na thin films and single crystals change their quasi-insulating intrinsic conductivity to a highly conductive p-type conductivity. With the increase of Na + doping concentration, the grain size of the film increases, the surface becomes smoother, and the crystallinity improves. The highly conductive p-type sodium-doped CH 3NH 3PbI 3 (MAPbI 3: Na) perovskite single crystals and thin films are successfully grown using the inverse temperature crystallization (ITC) method and antisolvent spin-coating (ASC) method, respectively.
![na xps peak na xps peak](https://sales.xpssimplified.com/_images/element-indium-xpsspectra.png)
To regulate the optical and electrical properties of the crystals and films of the intrinsic methylammonium lead iodide (CH 3NH 3PbI 3), we dope them with sodium (Na) by selecting sodium iodide (NaI) as a dopant source. 2School of Materials Science and Engineering, University of Jinan, Jinan, China.1School of Physics and Physical Engineering, Qufu Normal University, Qufu, China.Yujiao Li 1, Chen Li 2, Huanqin Yu 2, Beilei Yuan 2, Fan Xu 1, Haoming Wei 1 and Bingqiang Cao 1,2 *