Modulated surface photovoltage (SPV) spectra have been correlated with the phase composition in layers of CH3NH3PbI3 (MAPbI3) prepared from MAI and PbCl2 and annealed at 100 °C. Depending on the annealing time, different compositions of MAPbI3, MAPbCl3, MACl, PbI2, and an un-identified phase were found. It has been demonstrated that evaporation of MAI and HI is crucial for the development of electronic states in MAPbI3 and that only the appearance and evolution of the phase PbI2 has an influence on electronic states in MAPbI3. With ongoing annealing, (i) a transition from p- to n-type doping was observed with the appearance of PbI2, (ii) shallow acceptor states were distinguished and disappeared in n-type doped MAPbI3, and (iii) a minimum of the SPV response related to deep defect states was found at the transition from p- to n-type doping. The results are discussed with respect to the further development of highly efficient and stable MAPbI3 absorbers for solar cells.
Perovskite materials show excellent photovoltaic performance along with simple processing and low‐energy requirements. Despite their high power conversion efficiency (PCE), instability in the presence of moisture is still a major challenge. An effective method to enhance perovskite stability is by reducing dimensionality through incorporation of long organic cations into the perovskite crystal, which improves charge‐carrier extraction efficiency of the perovskites compared to conventional 3D perovskites. Quasi‐2D perovskites or 2D/3D perovskites strike a good balance between PCE and stability, having much improved stability compared to 3D structures while retaining excellent optoelectronic properties. Yielding better thermal stability and broader absorption into the near‐infrared, formamidinium iodide (FAI) doping has positive influences yet tends to cause poor surface morphology. Here, we introduce highly stable MA/FA‐based quasi‐2D perovskite fabricated by mixed cation doping (MCD), which is repeated deposition of MA and FA cations onto a quasi‐2D perovskite layer. MCD enables better morphology and surface passivation, leading to fewer defects. MA/FA‐based quasi‐2D perovskite with quasi‐cubic structure has high humidity resistivity, remaining intact after 90 days under 60% relative humidity without encapsulation. The underlying mechanism is further explained by binding and formation energies of cation mixture in solution and perovskite structure through computational analysis.
Perovskite materials are emerging as suitable materials for low-cost, high efficiency optoelectronics. In this study, we reported the surface modification of 2D (PEA)2PbBr4 for violet emission using PEG doping followed by a newly developed step called swift cation doping (SCD) where phenylethylammonium cations (PEA+) in isopropanol (IPA) are abruptly applied during crystallization. 2D Perovskite doped with PEG using SCD resulted in smaller grain, smoother surface, higher film density, higher photoluminescence quantum efficiency, and longer average PL lifetime. These features are highly beneficial for photoluminescence application and can be easily applied to enhance other perovskite LED thin films.
Rapid advancements in perovskite materials have led to potential applications in various optoelectronic devices, such as solar cells, light-emitting diodes, and photodetectors. Due to good photoelectric properties, perovskite enables low-cost and comparable performance in terms of responsivity, detectivity, and speed to those of the silicon counterpart. In this work, we utilized triple cation perovskite, well known for its high performance, stability, and wide absorption range, which is crucial for broadband photodetector applications. To achieve improved detectivity and faster response time, graded multilayer perovskite absorbers were our focus. Sequential spray deposition, which allows stacked perovskite architecture without disturbing lower perovskite layers, was used to generate single, double, and triple-layer perovskite photodetectors with proper energy band alignment. In this work, we achieved a record on self-powered perovskite photodetector fabricated from a scalable spray process in terms of EQE and responsivity of 65.30% and 0.30 A W-1. The multilayer devices showed faster response speed than those of single-layer perovskite photodetectors with the champion device reaching 70 µs and 88 µs for rising and falling times. The graded band structure and the internal electric field generated from perovskite heterojunction also increase specific detectivity about one magnitude higher in comparison to the single-layer with the champion device achieving 6.82 × 1012 cmHz1/2 W−1.
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