Perovskite-based semiconductors,
such as methylammonium and cesium
lead halides (MPbX3: M = CH3NH3
+ or Cs+; X = I–, Br–, or Cl–), have attracted immense attention for
several applications, including radiation detection, due to their
excellent electronic and optical properties.1,2,3,4,5,6 In addition, the combination of perovskites with other materials
enables unique device structures. For example, robust and reliable
diodes result when combined with metal oxide semiconductors. This
device can be used for detection of nonionizing and ionizing radiation.
In this paper, we report a unique perovskite single-crystal-based
neutron detector using a heterojunction diode based on single-crystal
MAPbBr3 and gallium oxide (Ga2O3)
thin film. The MAPbBr3/Ga2O3 diodes
demonstrate a leakage current of ∼7 × 10–10 A/mm2, an on/off ratio of ∼102, an
ideality factor of 1.41, and minimal hysteresis that enables alpha
particle, gamma-ray, and neutron detection at a bias as low as (−5
V). Gamma discrimination is further improved by 85% by optimizing
the thickness of the perovskite single crystal. The MAPbBr3/Ga2O3 diodes also demonstrate a neutron detection
efficiency of ∼3.92% when combined with a 10B neutron
conversion layer.
A small cross-section of silver nanoparticles (AgNPs) placed at the rear-part of the solar cell avoids the parasitic absorption of the nanoparticles which is the biggest barrier for plasmonic structures when acting as photocurrent enhancers. Herein, we demonstrate p-i-n planar perovskite solar cells with the structure ITO/PEDOT:PSS/MAPbI3/PCBM/Ni:Au, where the PCBM electron extraction layer (EEL) was intentionally modified with variable amounts of AgNPs. The addition of small amounts of AgNPs (e.g., 5 wt. %) into the PCBM improved the overall reproducibility and reliability of the solar cell fabrication process after optimization. Plasmonic simulations suggest that any plasmonic-optical effects are relatively small compared to sample absorbance due to perovskite alone. It has been concluded that plasmonic-electrical effects play a major role in averaged performance improvement. Therefore, the addition of small AgNPs in low concentration to the EEL layer accounts for higher Jsc, Voc and FF as a result of a better perovskite coverage by the EEL and an improved charge carrier collection as evidenced by morphological and electrical analysis.
Hybrid organic-inorganic lead halide perovskite materials show great promise in a number of optoelectronic applications, including solar cells, light emitting diodes, and photodetectors. Understanding their intrinsic material properties is critical to enhancing device performance and enabling innovative material and device designs. Here, we study lattice dynamics using far-infrared (FIR) reflectance and photogenerated carrier dynamics using surface photovoltage (SPV) measurements on high-quality methylammonium lead bromide (MAPbBr3) single crystals. FIR reflectance shows three coherent infrared-active phonon modes between 40 and 200 cm−1 that result in reststrahlen bands with much higher peak reflectance than has been previously reported. The phonon mode strength and damping are comparable to classical oxide perovskite single crystals. However, the effects of defects on photogenerated carrier recombination are still evident in SPV measurements. By performing SPV over different spectral ranges, we are able to separate the effects of surface and bulk defects on the recombination dynamics of photogenerated charge carriers. We further apply SPV measurements to obtain the minority carrier (electron) diffusion length for the MAPbBr3 crystal. This study demonstrates that both FIR reflectance and SPV measurements provide useful information on the electromagnetic response properties of halide perovskite single crystals.
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