Doping and Photon Induced Defect Healing of Hybrid Perovskite Thin Films: An Approach Towards Efficient Light Emitting Diodes

Abstract

Here, we demonstrate a simple method to improve photoluminescence and electroluminescent properties of MAPbBr3 perovskite thin films by monovalent Cs cation doping and treatment with UV light. It is known that the intermediate species of lead halides, which limits the photoluminescence quantum yield (PLQY) of perovskite thin films, are formed due to the presence of an organic polar solvent. In such cases, coalescence of nanocrystals is unavoidable when the thin‐films are thermally annealed to remove the intermediate phases and solvent residues. We find that PbBr2(DMSO)x complexes can effectively tune the morphology, grain boundary, PLQY, and non‐radiative loss of perovskite thin films under UV light irradiation. Upon UV exposure, highly uniform MA0.87Cs0.13PbBr3 ultra‐thin (45 nm) films with a full surface coverage of neatly packed nanocrystallites are obtained. When these films are integrated into electroluminescent devices, a current efficiency (CE) of 18.71 Cd/A and an external quantum efficiency (EQE) of 5.63% are observed for green perovskite‐based light emitting diodes (PeLEDs). These values of CE and EQE are respectively thirty‐four and forty‐three times higher than those achieved in pure MAPbBr3 based devices.

Stabilizing the Electroluminescence of Halide Perovskites with Potassium Passivation

“…In particular, the stability of perovskite devices has been associated with moisture/heat instability of the A-site organic cation in the ABX3 perovskite crystal structure (where A is a monovalent cation (methylammonium (MA + ), formamidinium (FA + ) or cesium (Cs + )), B is a divalent cation (Pb 2+ , Mn 2+ or Zn 2+ ), and X is a halide anion (I -, Bror Cl -)), joule heating at operational bias, and halide ion migration. [9][10][11][12][13][14][15][16][17][18] Numerous approaches have been employed to remove joule heating by using thermally stable materials and to suppress ion migration by doping or mixing with poly(ethylene oxide) (PEO), 19,20 phenylethylammonium (PEA), 21 (9,9-bis(3-(N,Ndimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene) (PFN), 22 and 3,3diphenylpropylamine bromide (DPPA-Br), 23,24 . Additionally, improving structural stability by substitution or doping of A-(MA + , FA + , Cs + ), and B-(Pb 2+ , Mn 2+ , Zn 2+ , Ce 3+ ) site cations have been explored.…”

“…Additionally, improving structural stability by substitution or doping of A-(MA + , FA + , Cs + ), and B-(Pb 2+ , Mn 2+ , Zn 2+ , Ce 3+ ) site cations have been explored. [10][11][12][13][14][15][16][17][18] Various efforts have also been made in tuning the dimensionality of the perovskite by substituting the A-site cations with organic additives and long chain ammonium salts such as alkyl ammonium, 25 phenylethylammonium, [26][27][28][29] 1naphthylmethylammonium, [30][31][32] and phenylbutylammonium 33 to improve the device performance. All-inorganic perovskites, having higher decomposition temperatures, also benefit from higher operational stability.…”

“…Halide perovskites are undergoing a rapid development for optoelectronic applications, particularly in solar cells (PSCs) , and light-emitting diodes (PeLEDs). , The power conversion efficiencies (PCEs) of PSCs have recently been shown to exceed 25%, while the external quantum efficiencies (EQEs) of PeLEDs exceeding 20% for both green and red and 10% for blue have been reported within a short span of time. − However, the quest for stabilizing perovskite devices has been challenging and requires continuous investigation into different aspects of compositional chemistry for the perovskite compound. In particular, the stability of perovskite devices has been associated with moisture/heat instability of the A-site organic cation in the ABX 3 perovskite crystal structure [where A is a monovalent cation (methylammonium (MA + ), formamidinium (FA + ), or cesium (Cs + )), B a divalent cation (Pb 2+ , Mn 2+ , or Zn 2+ ), and X a halide anion (I – , Br – or Cl – )], joule heating at operational bias, and halide ion migration. − Numerous approaches have been employed to remove joule heating by using thermally stable materials and to suppress ion migration by doping or mixing with poly­(ethylene oxide) (PEO), , phenylethylammonium (PEA), (9,9-bis­(3-( N , N -dimethylamino)­propyl)-2,7-fluorene)- alt -2,7-(9,9-dioctylfluorene) (PFN), and 3,3-diphenylpropylamine bromide (DPPA-Br). , Additionally, improving structural stability by substitution or doping of A- (MA + , FA + , Cs + ) and B- (Pb 2+ , Mn 2+ , Zn 2+ , Ce 3+ ) site cations have been explored. − Various efforts have also been made in tuning the dimensionality of the perovskite by substituting the A-site cations with organic additives and long-chain ammonium salts such as alkyl ammonium, phenylethylammonium, − 1-naphthylmethylammonium, − and phenylbutylammonium to improve the device performance. All-inorganic perovskites, having higher decomposition temperatures, also benefit from higher operational stability.…”

Composition engineering to obtain efficient hybrid perovskite light-emitting diodes

“…Among the various perovskite components, MAPbBr 3 has great potential for preparing high-efficiency Pero-LEDs. However, it is reported that the most primitive perovskite films comprising MAPbBr 3 (i.e., PbBr 2 :MABr = 1:1) exhibit low surface coverage, poor structural stability, and poor crystalline quality with too many nonradiative defects [24,25]. To improve the film quality of MAPbBr 3 perovskite, Lee et al precisely adjusted the molar proportion of MABr and PbBr 2 [4].…”