Spin Coating Method and Vapor Deposition Method are commonly used in the preparation of rare earth doped perovskite thin films^[16].

The spin coating method is to spin coat the perovskite precursor solution on the substrate, and then heat or introduce an antisolvent to increase the supersaturation of the precursor solution to induce crystallization to form a dense and uniform film (Figure 1A). Duan et al. Finally obtained CsPbBr₃:RE³⁺(RE³⁺=Yb³⁺, Er³⁺, Ho³⁺, Tb³⁺, Sm³⁺) films by spin coating rare earth ions with lead bromide in N, N-dimethylformamide followed by addition of cesium bromide in alcohol^[17].

Spin coating is a common method for preparing halide and oxide perovskite thin films, which has the advantages of small and controllable film thickness, high surface flatness, high crystallinity, few defects, low pollution, large yield and high efficiency. At present, this method has been widely used in the preparation of solar cell films and other films^[18].

Vapor deposition methods include multi-source co-deposition and single-source deposition, in which raw materials are transported in vapor phase to form a coating on the surface of a substrate. Crane et al. Prepared CsPb(Cl_1-xBr_x)₃:Yb³⁺ thin films using a single-source vapor deposition method^[19]. The CsPb(Cl_1-xBr_x)₃:Yb³⁺ powder was selected as the raw material, and the thin films with the thickness of 50 – 1000 nm were obtained by heating and sublimation.

Chemical vapor deposition (CVD) is a technology that uses gaseous or vaporous substances to react in the gas phase or at the gas-solid interface to form solid deposits. This technology has the advantages of simple operation and controllable reaction, so it is widely used in high-quality material synthesis experiments^[20].

The main methods of synthesizing perovskite powder are Mechanochemical Synthesis Method, Thermal Annealing Method and Precipitation Method^[21].

The mechanochemical method usually uses a ball mill (Fig. 2C) or a mortar to grind halide raw materials to prepare perovskite powder. For example, Aleksanyan et al. Prepared CsPbI₃:Nd³⁺ powder by ball milling, and found that NdI₃ doping could prevent phase transformation^[22].

The thermal annealing method is to place the halide raw materials at a high temperature so that they can fully diffuse and react to form perovskite powder. Stefanski et al. Selected YbCl₃·6H₂O as the rare earth doping source and synthesized CsPbCl₃:Yb³⁺ powder by thermal annealing^[23]. A small amount of methanol is added to the raw materials, mixed, ground and evaporated, and then the mixture is thermally annealed to obtain the CsPbCl₃:Yb³⁺ powder.

The precipitation method is to obtain perovskite powder by cooling and stirring the precursor or dropping the precursor into an antisolvent and then rapidly precipitating the precursor (fig. 2D). Dagnall et al. Used cesium chloride and lead chloride as raw materials and YbCl₃·6H₂O as rare earth doping raw materials^[24]. Tirring and evaporating to obtain intermediate powder, grinding the intermediate powder, and annealing at high temperature to obtain CsPbCl₃:Yb³⁺ powder.

The advantage of precipitation method is that it is easy to prepare nano-powder materials with small particle size and uniform distribution. However, the disadvantage is that the addition of precipitant may cause local concentration to be too high, resulting in agglomeration or uneven composition.

At present, the main processes for growing perovskite single crystals include melting Method such as Bridgman Method, solution method such as Hydrothermal method, Inverse Temperature Crystallization (ITC), Antisolvent Vapor-assisted Crystallization (AVC) and Solvent Evaporation^{[25][26][27][28][29]}.

The Bridgman method is a simple and practical method for single crystal growth (Fig. 2 e). A halide raw material or a perovskite polycrystalline material is melted, and the raw material in a molten state is solidified into a target phase. Bridgman method is often used for inorganic perovskite single crystal growth. Taking the growth of inorganic lead-based 3D perovskite CsPbBr₃ as an example, Kanatzidis et al. Used the vertical Bridgman method to grow CsPbBr₃ single crystals in a three-temperature zone growth furnace^[30]. Zhang et al. Further optimized the growth conditions, reduced the Pb-CsPbBr₃ rich phase with local stoichiometry deviating from CsPbBr₃, and further improved the quality of the single crystal^[31]. Examples of rare earth ion doping by Bridgman method have been reported in the literature, including CsPbCl₃:La³⁺, CsPbCl₃:Dy³⁺, CsPbCl₃:Er³⁺, CsPbCl₃:Yb³⁺ and Cs₄PbBr₆:Pr³⁺ single crystals^{[32][33][34][35][36]}. CsX of 5 N grade purity and PbX₂ halide or CsPbX₃(X=Cl, Br, I) perovskite are usually used as raw materials, and anhydrous rare earth halide is used as doping source. The atomic ratio of RE/Pb in that raw material is 0.3 to 3%.

The crystal growth method in solution can also grow large-size lead halide perovskite single crystals, as shown in Figure 2G ~ H. The liquid phase growth method has a growth rate and a crystal product size similar to or even better than those of the melt method. For example, Ma et al. Grown single crystals of MAPbI₃, MAPbBr₃, FAPbBr₃, etc., exceeding the size of a 1 cm² in about a day by adding a polymer to control nucleation and growth^[37]. Wang et al. Used the surface tension of the solution to grow the BA₂PbBr₄(BA=C₄H₁₂N⁺) single crystal film at the gas-liquid interface, and the crystal area reached 38 cm² and the thickness was 78 nm^[38]. Rong et al. Used dichlorosilane as an antisolvent to volatilize into the MAPbBr₃:Er³⁺ perovskite precursor solution by the AVC method, in which the ErCl₃ was fed at a ratio of Er/Pb = 1%^[39]. The final single crystal size is 7 mm × 7 mm × 2 mm. Hydrothermal method is a traditional crystal synthesis method, and the conditions of high temperature and high pressure improve the degree of solute ionization and the rate of chemical reaction^[40]. Zi et al. Improved the solvothermal method for MAPbI₃:RE³⁺, and continued the reaction of the prepared precursor at 180 ° C, and finally slowly cooled the temperature for crystallization to obtain 4~5 mm² sized MAPbI₃:RE³⁺(Yb³⁺,Er³⁺,Yb³⁺/Er³) single crystal^[41].

Hydrothermal method, as a mild synthesis method, allows co-condensation of different metal cations to obtain perovskites. However, the crystal grown by hydrothermal method is also sensitive to reaction temperature and time^[42].

Hot Injection and Ligand-assisted reprecipitation (LARP) are the main methods for nanocrystallization^[43][44].

The hot injection method (Figure 2 I) is a method in which the precursor solution containing part of the reactants is heated to 150 ~ 250 ℃ in an inert atmosphere, and then other reactants are injected to obtain perovskite crystals by rapid nucleation and growth controlled by ligands such as oleylamine and oleic acid. Kovalenko et al. First used the hot injection method to synthesize CsPbX₃ nanocrystals^[43]. Cesium carbonate is used as a cesium source, 1-octadecene is used as a high-boiling-point solvent, oleic acid is used as the ligand, and the CsPbX₃ nanocrystal is obtained by further crystallization through ice-water bath cooling. Pan et al. Used a hot injection method to synthesize rare earth doped CsPbCl₃ nanocrystals^[45]. Oleic acid and oleylamine are used as ligands, rare earth chloride hexahydrate is used as a doping agent,CsPbCl₃:RE³⁺(RE³⁺=Ce³⁺, Sm³⁺, Eu³⁺,Tb³⁺, Dy³⁺, Er³⁺, Yb³⁺) nanocubes. With the increase of the atomic number of the doped ions, the size of the nanocrystals decreases.

The ligand-assisted precipitation method can be carried out at room temperature under an air atmosphere (Fig. 2j). Perovskite nanocrystals were obtained by dropping the precursor solution into a non-polar solvent (toluene, n-hexane, dichloromethane) with the assistance of ligands. Zhang et al. Used oleylamine and oleic acid as ligands, dropped toluene and stirred to obtain CsPbX₃ nanocrystals^[44]. Liu et al. Obtained MAPbBr₃:Eu²⁺ crystals at room temperature using EuBr₂ as the rare earth doping source, oleylamine and oleic acid as the ligands, and toluene as the anti-solvent^[46].

In addition to the above doping methods of introducing rare earth ions into the precursor, rare earth doping can also be achieved by ion exchange. Ion exchange method refers to the introduction of other ions into the pre-synthesized perovskite solution to change the ionic composition of perovskite. Debnath et al. Have dissolved rare earth ions (Nd³⁺, Sm³⁺, Eu³⁺,DMF of Tb³⁺, Dy³⁺, Yb³⁺) was dropped into the pre-synthesized CsPbBr₃ nanocrystals,The rare earth (Nd, Sm, Eu, Tb, Dy, Yb) doped CsPb(Br/Cl)₃ nanocrystals were obtained after standing for a period of time at room temperature followed by centrifugation^[47].

The hot injection method has the advantages of short reaction time and rapid crystal nucleation, and the size of the synthesized perovskite nanocrystal is uniform and adjustable. However, the hot injection method is not suitable for large-scale production because of its high environmental requirements (inert gas protection) and low synthesis yield^[48].

Rare earth ion doped cesium lead halide perovskite in ion exchange method can control the band gap of the host through halide ion exchange, achieve energy matching, and better produce energy transfer from perovskite to rare earth ions. The method is simple, can occur in the environment, has a fast reaction rate, and has been widely used in the synthesis of rare earth doped CsPbX₃ nanocrystals^[48].

Zheng et al. Prepared MAPbBr₃:Nd³⁺ thin films by spin coating, and observed that Nd³⁺ had a significant effect on the nucleation and growth of perovskite^[49]. The addition of Nd³⁺ led to heterogeneous nucleation and improved the crystallinity of perovskite films. Compared with homogeneous nucleation, heterogeneous nucleation has lower nucleation energy and higher nucleation rate. The crystal growth process is relatively separated from the nucleation process, resulting in the formation of crystals with high phase purity and fewer defects. The MAPbBr₃:Nd³⁺ photoluminescence quantum yield (PLQY) was enhanced by a factor of 6 and remained PLQY stable for at least 8 months under ambient conditions. Wang et al. Introduced Eu³⁺-Eu²⁺ ion pairs in MAPbI₃ solar cells^[50]. The ion pair acts as a "redox shuttle" while selectively oxidizing Pb⁰ and reducing I⁰ defects. At the same time, the crystallinity of the film is improved. The final device achieved a PCE of 21.52% with long-term durability. Yang et al. Added GdF₃ to spin-coated perovskite films and annealed them in aminobutanol atmosphere. The introduction of Gd produced a redox shuttle effect and optimized the Oswald ripening crystallization process^[51]. Finally, a high-performance solar cell with a PCE of 21.21% is obtained.

Wu et al. Added different proportions of europium acetate (Eu(AcO)₃) during the synthesis of CsPbCl₃ by hot injection method, and found that the CsPbCl₃ nanocrystals changed from cubic morphology to nanowires with the growth direction of (200) under the induction of Eu(AcO)₃^[52]. X-ray photoelectron spectroscopy (XPS) shows that the doping sites of Eu³⁺ are located on the surface of the nanocrystals. Combined with density functional theory (DFT) calculations, the co-adsorption of AcO^- and Eu³⁺ on the crystal surface regulates its growth and passivates the defects. The responsivity and detectivity of the prepared UV detector are 398 mA/W and 3.3×10¹¹Jones, respectively.

Lei et al. Used the sonochemical method to sonicate the precursor solution with the addition of EuBr₂ to synthesize CsPbBr₃/Cs₄PbBr₆:Eu composite nanocrystals^[53]. The X-ray diffraction pattern (XRD) illustrated that the EuBr₂ induced the phase transformation from CsPbBr₃ to Cs₄PbBr₆ and formed the CsPbBr₃/Cs₄PbBr₆ composite structure crystal. Eu²⁺ is oxidized to Eu³⁺ during synthesis. Meanwhile, Eu³⁺ forms a Eu (DMF {)}_x^{3+} complex with N, N-dimethylformamide. The Eu (DMF) {)}_x^{3+} regulates the ion concentration in the solution and coordinates with the surface of the Cs₄PbBr₆ crystal to inhibit the growth rate _, of the CsPbBr₃ phase, thereby promoting the formation of the Cs₄PbBr₆ phase.

In terms of single crystals, Wang et al. Grew CsPbBr₃:Y³⁺ single crystals by the ITC-method^[54]. The Y doping concentration at different positions of the single crystal sample was measured by atomic emission spectroscopy (ICP), and the results showed that the concentration at the outer edge of the crystal was higher than that at the inner part of the crystal. Lin et al. Prepared MAPbI₃:Ce³⁺ single crystal and polycrystalline thin films^[55]. The doping increases the carrier concentration and decreases the mobility of the film. Time-of-flight mass spectrometry (TOF-SIMS) results show that the surface Ce concentration of the MAPbI₃:Ce³⁺ is much higher than the bulk Ce concentration at 800 nm depth. These results all illustrate that the Ce³⁺ ion doping occurs only on the surface of the MAPbI₃ crystal.

In terms of nanocrystals, Ma et al. Synthesized CsPbCl₃:Yb³⁺ nanocrystals by hot injection method^[56]. Repeated centrifugal separation was used to distinguish nanocrystals of different sizes, and it was found that nanocrystals of different sizes had significant doping concentration differences. Time-resolved photoluminescence (TRPL) and positron annihilation lifetime spectroscopy (PALS) measurements show that the defects in the high concentration doped crystals are more than those in the low concentration doped crystals. The authors believe that increasing the number of defects in the CsPbCl₃ crystal can increase the doping concentration of Yb³⁺.

Generally, after doping with ions, the lattice of perovskite crystal is contracted or expanded, which will lead to the shift of XRD peaks. However, the recent study of trivalent rare earth (Ⅲ) ion doping in lead-based (Ⅱ) perovskite crystals shows that the lattice parameters of lead-based (Ⅱ) perovskite crystals are not significantly changed by trace trivalent rare earth (Ⅲ) ion doping, and the corresponding interplanar spacing in high-resolution transmission electron microscopy atomic images is also very small^[57,58][59].

The ionic radius of trivalent rare earth ions is closer to that of lead ions than that of A-site ions and halide ions. The radius of lead ion is 119 pm, and the radius of trivalent lanthanide ion is 86 ~ 103 pm. Therefore, the rare earth ions are more likely to replace the Pb ions in the host lattice. He et al. Calculated the defect formation energy in the orthorhombic phase CsPbBr₃:Ce³⁺ using first principles^[60]. The results show that it is more likely to replace the position of the Pb²⁺ than the Ce³⁺ to enter the gap and replace the Cs⁺,Ce³⁺. The cell parameters of CsPbBr₃ after surface doping by rare earth ions (Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb) to replace part of the cell model of Pb²⁺ are designed to remain basically unchanged.

Quantum cutting refers to a process in which a material absorbs a high-energy photon and converts it into two or more low-energy photon emissions. Milstein et al. And Li et al. Have proposed a physical model of the doped local structure of Yb³⁺-V_Pb-Yb³⁺ based on the Quantum cutting effect found in CsPbCl₃:Yb³⁺ (Figure 3A)^[61][62]. The Yb³⁺-V_Pb-Yb³⁺structure is consistent with a quantum-tailored energy transfer process, in which the CsPbCl₃ host absorbs a single high-energy photon, and the photon energy is converted into two emitted photons of 1.25 eV (980 nm) photon energy via energy transfer to two nearby Yb³⁺ luminescence centers.

Zhou et al. Synthesized CsPbCl₃:Yb³⁺ nanocrystals with actual doping concentrations ranging from 2.1% to 5.7% using the hot injection method by increasing the YbCl₃·6H₂O charge of the rare earth compound in the precursor^[63]. The sample with 5.7% doping concentration has an XRD shift of 0.06 ° on the (100) crystal plane. The interplanar spacing of the sample (100) was measured by high-resolution transmission electron microscopy (HRTEM), and it was found that the interplanar spacing decreased from 5.5151 Å to 5.3636 Å with the increase of Yb³⁺ doping concentration from 2.1% to 5.7% (Figure 3C). In addition, Cao et al. Attempted to locate the doping sites of CsPbBr₃:Lu³⁺ nanosheets by high-angle annular dark-field scanning transmission microscopy (HAADF-STEM), and found that the signals of some B-site ions on the (001) crystal plane had intensity differences, indicating that they might be the spatial sites where Lu³⁺ replaced Pb^2+[64].

XPS can be used to analyze the binding energy of each ion in the crystal, so it is often used to analyze the doping sites of rare earth ions in rare earth doped perovskites^[65,66]. For example, Sun et al. Used the hot injection method to synthesize CsPbCl₃:Sm³⁺ nanocrystals^[67]. The binding energy spectrum peaks of ³d_3/2, ³d_5/2, ⁴d_3/2, ⁴d_5/2 from Sm³⁺ were detected under XPS,Where ³d_3/2,³d_5/2 comes from SmCl₃ at the crystal surface and ⁴d_3/2,⁴d_5/2 comes from Sm³⁺ after entering the lattice. In addition, the XPS binding energy spectrum peaks of ⁴f_5/2 and ⁴f_7/2 of sample Pb²⁺ obviously move to the low energy direction after doping (Fig. 3 B), while the binding energy of Cs⁺ and Cl^- is weakly affected. This proves that Sm³⁺ is more likely to replace the site of Pb²⁺ in the crystal lattice.

Kluherz et al. Used synchrotron radiation fine absorption spectroscopy (XAS) and X-ray total scattering-differential pair distribution function method (dPDF) to systematically study the structural change of CsPbCl₃:Yb³⁺ single crystal prepared by melt method, and the X-ray absorption fine structure spectroscopy (EXAFS) showed that the coordination environment of Yb³⁺ in the single crystal prepared by melt method was octahedral, which indicated that the Yb³⁺ ion replaced the position of Pb²⁺ ion^[68]. At the same time, the bond length of Yb-Cl is observed to be 2.5858 Å in the dPDF spectrum, which is different from the bond length of Pb-Cl of 2.8383 Å, which is consistent with the EXAFS result after Fourier transformation. By comparing the experimental data with the simulation results of multiple types of vacancies, the V_Pb vacancy exists inside the CsPbCl₃:Yb³⁺ single crystal. Therefore, V_Pb is likely to be the main charge compensation mechanism for the heterovalent doping of CsPbCl₃:Yb³⁺.

Different crystal morphologies may lead to differences in doping results. Roh et al. Synthesized CsPbCl₃:Yb³⁺ single crystals and nanocrystals by melt method and thermal injection method^[35]. The photoluminescence spectra at low temperature show that the partial characteristic emission peak of the Yb³⁺ in the range of 978.5 ~ 982.3 nm is different between the single crystal and the nanocrystal, which indicates that the local electronic structure of the Yb³⁺ doping may be different between them.

The study of composition distribution shows that the distribution of rare earth ions is related to the crystal morphology and synthesis conditions, which has guiding significance for the realization of homogeneous phase doping and controllable surface doping. A series of studies have explored the doping sites, the introduction of related defects, and the charge compensation mechanism of Yb³⁺ and Lu³⁺, which are two rare earth ions with small ionic radii, in perovskite, indicating that trivalent rare earth ions can replace lead ions and produce V_Pb to achieve charge compensation.

The carrier species and the change of Fermi level can be determined by Hall effect measurement, ultraviolet photoelectron spectroscopy (UPS), scanning tunneling microscopy (STS), Kelvin probe microscopy (KPFM) and other techniques.

Lin et al. Studied the surface doping of MAPbI₃ perovskite by AgBr, SrI₂, CeI₃^[55]. Undoped MAPbI₃ behaves as a p-type semiconductor. After the perovskite thin film is treated by AgBr,SrI₂,CeI₃, the majority carrier type of the MAPbI₃ thin film changes from holes to electrons, that is, from p-type semiconductor to n-type semiconductor. TOF-SIM test shows that the rare earth doping stays on the surface of the crystal, which greatly increases the dark current on the surface of the crystal. It is difficult for impurity ions to enter the perovskite crystal, and the intrinsic p-type semiconductor characteristics are maintained in the crystal. For the rare earth Ce³⁺ ion, this may be correlated with its ionic hardness that distinguishes it from Pb^2+[83]. After the surface of the MAPbI₃ film is treated by CeI₃, the carrier type of the film is changed from hole to electron, and from p-type semiconductor to n-type semiconductor. The contact potential difference (CPD) was measured by KPFM after partial annealing of MAPbI₃ single crystal wafer by CeI₃ particle treatment. The annealing treatment leads to a decrease in the work function and a shift of the Fermi level to the conduction band, transforming into an n-type semiconductor. At present, the conventional donor doping ion of lead halide perovskite is Bi³⁺, which will directly reduce the band gap of perovskite and introduce deep traps, which has a negative impact on the photoelectric properties^[84]. However, the surface doping of Ag⁺, Sr²⁺ and Ce³⁺ did not cause the performance degradation and band gap change. The calculation shows that the doping of metal ions increases the electronic States at the conduction band edge of perovskite, and finally presents donor doping.

Liu et al. Fabricated polycrystalline CsPbBr₃:Eu³⁺ solar cells^[85]. After doping, the grain size of the CsPbBr₃ becomes larger, the grain size is uniform, and the grain boundary is obviously reduced. UPS shows that the Fermi level of CsPbBr₃ increases from-3. 71 eV to-3. 65 eV after doping 3%Eu³⁺. The top of the valence band decreases from -5.92 eV to -6.20 eV, and the bottom of the conduction band decreases from -3.61 eV to -3.64 eV. The change of energy band optimizes the barrier of CsPbBr₃:Eu³⁺ at the interface of carbon electrode, which is beneficial to the transport of carriers, and the final doped device achieves a maximum PCE of 8. 06%. Yang et al. Selected samarium acetylacetonate (Sm(acac)₃) as a dopant to prepare CsPbI₂Br perovskite thin films by a one-step spin-coating method^[86]. The results of XPS and TOF-SIM showed that some Sm³⁺ replaced the position of Pb²⁺. The UPS results indicate that the VBM of undoped CsPbI₂Br and Sm(acac)₃ doped CsPbI₂Br are − 6.05 eV and − 6.15 eV, respectively. Combined with the band gap values, the conduction band energies of CsPbI₂Br and Sm(acac)₃ doped CsPbI₂Br are deduced to be − 4.17 eV and − 4.26 eV, respectively. The introduction of samarium acetylacetonate optimized the perovskite film quality and passivated the perovskite solar cell device interface (Figure 5B), resulting in a PCE of 12.86%. Moreover, the doped device shows excellent thermal stability, and can still maintain 90% of the initial PCE after being placed at 85 ℃ for 200 hours. Parveen et al. Doped MAPbBr₃ nanosheets with Eu³⁺ by solvothermal method^[87]. Under the feeding of 10%(RE/Pb=10%)EuCl₃, the size of MAPbBr₃ nanosheets became larger and the thickness became thinner. The band gap of MAPbBr₃ increases from 2. 39 eV to 2. 94 eV with the increase of doping concentration, which may be related to the change of nanocrystal size. The Eu-doped MAPbBr₃ nanosheets eliminated part of the trap States and promoted the rapid charge transport. The resulting MAPbBr_2.7Cl_0.3:Eu³⁺ photodetector exhibits self-bias behavior at 405 nm excitation with an on-off ratio exceeding that of 10³. The responsivity reaches 5.29 A/W at 5 V bias, and the detectivity reaches 1.06×10¹²Jones.

Carrier properties include carrier concentration, carrier mobility, carrier lifetime. Carrier concentration and mobility can be measured by Hall effect test, and carrier mobility can also be measured by space charge limited current test (SCLC). The carrier lifetime can be obtained by TRPL and transient photovoltage (TPV) characterization.

Rong et al. Fabricated a photodetector based on MAPbBr₃:Er³⁺ single crystal, and the conductivity was improved by a factor of two relative to the undoped one^[39]. Doping Er³⁺ into the MAPbBr₃ increases the carrier mobility from 35±2 cm²/V/s to 96.10 cm²/V/s (Fig. 5C, d), and moreover, the trap density is reduced by 37%. The MAPbBr₃:Er³⁺ photodetector with planar interdigital gold electrodes has a self-powered characteristic, that is, it works without external voltage. Moreover, optimizing the crystal quality will also significantly improve the carrier mobility^[92,93]. Shen et al. Prepared 2D: 3D mixed PEA₂PbI₄∶MAPbI₃∶Nd³⁺ thin films using spin coating^[94]. Nd³⁺ was doped with two kinds of lead-based perovskites simultaneously. The doping of Nd³⁺ greatly changed the morphology of the film, making the 2D and 3D perovskite grains mixed more uniformly, and the grain size also increased. Grazing incidence small angle X-ray scattering (GIWAXS) results show that PEA₂PbI₄:MAPbI₃:Nd³⁺ has high crystallinity, which helps to improve the charge carrier mobility^[94]. The electron/hole mobility ratio of the doped film increases from μ_e/μ_h=0.34 to 0.62, indicating a better equilibrium carrier transport property. The fluorescence lifetime test shows that the doping has no significant effect on the fast component decay of 0. 48 ns, while the slow component decay increases from 8. 9 ns to 10 ns, indicating that the non-radiative recombination of photogenerated carriers is suppressed. The fabricated photodetector has a photoelectric response of more than 700 mA/W and a linear dynamic range of 165 dB. Zhao et al. Selected neodymium trifluoromethanesulfonate as the dopant to prepare solar cells with α-FAPbI:Nd³⁺ thin film as the absorber layer by spin coating^[95]. The fluorescence lifetime of the perovskite layer is prolonged at a very small doping ratio of (0.08%)Nd³⁺. The device's transient photovoltage (TPV) drop is slowed down as evidence of nonradiative defect reduction. In situ dynamic PL Mapping of the samples under 150 mV/μm bias electric field shows that the photoluminescence intensity of the undoped perovskite decreases sharply under current operation, while the sample doped with trace amount of Nd³⁺ remains consistent after 10 min. This proves that Nd³⁺ effectively suppresses the degradation of photoluminescence properties caused by ion migration. The solar cell fabricated by Nd³⁺ doping with α-FAPbI₃ achieved a PCE efficiency of over 20% and retained the original efficiency of 86.4% after 2002 H, which is significantly higher than that of the conventional doping ions (Ca²⁺ and Na⁺) used to suppress ion migration.