Photoluminescence: Local Versus Long-Range Diffusion Effects of Photoexcited States on Radiative Recombination in Organic-Inorganic Lead Halide Perovskites (Adv. Sci. 9/2015)

Perovskite and Conjugated Polymer Wrapped Semiconducting Carbon Nanotube Hybrid Films for High-Performance Transistors and Phototransistors

Although organic-inorganic halide perovskites continue to generate considerable interest due to great potentials for various optoelectronic devices, there are some critical obstacles to practical applications, including lead toxicity, relatively low field-effect mobility, and strong hysteresis during operation. This paper proposes a universal approach to significantly improve mobility and operational stability with reduced dual-sweep hysteresis for perovskite-based thin film transistors (TFTs) by coupling low-dimensional lead-free perovskite material (C₆H₅C₂H₄NH₃)₂SnI₄ (hereafter abbreviated as (PEA)₂SnI₄) with embedded conjugated polymer wrapped semiconducting carbon nanotubes (semi-CNTs). In (PEA)₂SnI₄/semi-CNT hybrid TFTs, semi-CNTs can provide highway-like transport paths, enabling smoother carrier transport with less trapping and scattering. We also demonstrate the performance of (PEA)₂SnI₄/semi-CNT hybrid phototransistors with ultrahigh photoresponsivity ( R) of 6.3 × 10⁴ A/W and detectivity ( D*) of 1.12 × 10¹⁷ Jones, which is about 2 or 3 orders of magnitude higher than that of the best devices available to date. The results indicate promising potentials for solution-processed perovskite/semi-CNT hybrid platforms, and the developed strategy can be applied for high-performance perovskite nanomaterial optoelectronics.

Imaging Electronic Trap States in Perovskite Thin Films with Combined Fluorescence and Femtosecond Transient Absorption Microscopy

Charge carrier trapping degrades the performance of organometallic halide perovskite solar cells. To characterize the locations of electronic trap states in a heterogeneous photoactive layer, a spatially resolved approach is essential. Here, we report a comparative study on methylammonium lead tri-iodide perovskite thin films subject to different thermal annealing times using a combined photoluminescence (PL) and femtosecond transient absorption microscopy (TAM) approach to spatially map trap states. This approach coregisters the initially populated electronic excited states with the regions that recombine radiatively. Although the TAM images are relatively homogeneous for both samples, the corresponding PL images are highly structured. The remarkable variation in the PL intensities as compared to transient absorption signal amplitude suggests spatially dependent PL quantum efficiency, indicative of trapping events. Detailed analysis enables identification of two trapping regimes: a densely packed trapping region and a sparse trapping area that appear as unique spatial features in scaled PL maps.