Proceedings Article | 18 September 2018
KEYWORDS: Perovskite, Photodetectors, Optoelectronics, Optoelectronic devices, Light emitting diodes, Quantum efficiency, Thin films, Photovoltaics, Semiconductors, Absorption
While the field of perovskite-based optoelectronics has mostly been dominated by photovoltaics, light-emitting diodes and transistors, semiconducting properties peculiar to perovskites make them interesting candidates for innovative and disruptive applications in light signal detection. Perovskites combine effective light absorption in the broadband range with good photo-generation yield and high charge carrier mobility, which combination provides promising potential for exploiting sensitive and fast photodetectors that are targeted for image sensing, optical communication, environmental monitoring, or chemical/biological detection. Currently, organic-inorganic hybrid and all-inorganic halide perovskites with controlled morphologies of polycrystalline thin films, nano-particles/wires/sheets, and bulk single crystals have shown key figure-of-merit features in terms of their responsivity, detectivity, noise equivalent power, linear dynamic range, and response speed. The sensing region has been covered from ultraviolet–visible–near infrared (UV–Vis–NIR) to gamma photons, based on two- or three-terminal device architectures. Diverse photoactive materials and devices with superior optoelectronic performances have stimulated attention from researchers in multidisciplinary areas. We offer a comprehensive overview of the recent progress of perovskite-based photodetectors, focusing on versatile compositions, structures, and morphologies of constituent materials, and diverse device architectures toward the superior performance metrics. Combining the advantages of both organic semiconductors (facile solution processability) and inorganic semiconductors (high charge carrier mobility), perovskites are expected to replace commercial silicon for future photodetection applications.
The optical and electronic properties of noble metallic nanoparticles can be exploited to enhance the performance of inorganic/organic photodetectors. We integrated a uniformly-distributed layer of Au nanorods (AuNRs) into vertically-structured perovskite photoconductive photodetectors and report, as a result, perovskite-AuNR hybrid photodetectors that exhibit significant photocurrent enhancements. Ultimately it achieves a responsivity of ~320 A/W at a low driving voltage of -1 V. This is an improvement of 60% compared to the responsivity of pristine devices (~200 A/W). The high responsivity and low driving voltage place this device among the highest-performing perovskite-based thin-film photoconductive photodetectors reported. We characterized the stability and linearity of the photoresponse following repeated light/dark cycles. The hybrid device also shows a fast response (with the decay time of ~95 ns) compared to pristine devices (~230 ns). The improvements in photodetection performance are attributed to plasmon-enhanced optical absorption, as well as advances in charge extraction and transport.
Metal halide perovskites have rapidly advanced thin film photovoltaic performance; as a result, the materials’ ob-served instabilities urgently require a solution. Using density functional theory (DFT), we show that a low energy of formation, exacerbated in the presence of humidity, explains the propensity of perovskites to decompose back into their precursors. We find, also using DFT, that intercalation of phenylethylammonium between perovskite layers in-troduces quantitatively appreciable van der Waals interactions; and these drive an increased formation energy and should therefore improve material stability. Here we report the reduced-dimensionality (quasi-2D) perovskite films that exhibit improved stability while retaining the high performance of conventional three-dimensional perovskites. Continuous tuning of the dimensionality, as assessed using photophysical studies, is achieved by the choice of stoi-chiometry in materials synthesis. We achieve the first certified hysteresis-free solar power conversion in a planar per-ovskite solar cell, obtaining a 15.3% certified PCE, and observe greatly improved performance longevity. The same protocol was applied to develop highly stable and efficient photodectors in diverse device configurations.
Organometal halide perovskites exhibit large bulk crystal domain sizes, rare traps, excellent mobilities, and carriers that are free at room temperature – properties that support their excellent performance in charge-separating devices. In devices that rely on the forward injection of electrons and holes, such as light-emitting diodes (LEDs), excellent
mobilities contribute to the efficient capture of nonequilibrium charge carriers to rare nonradiative centres. Moreover, the lack of bound excitons weakens the competition of desired radiative over undesired nonradiative recombination. Here we also report a perovskite mixed material, one comprised of a series of differently quantum-size-tuned grains, that funnels photoexcitations to the lowest-bandgap light-emitter in the mixture. The materials function as charge carrier concentrators, ensuring that radiative recombination successfully outcompetes trapping and hence nonradiative recombination. We use the new material to build devices that exhibit an external quantum efficiency (EQE) of 8.8% and a radiance of 80 Wsr-1m-2. These represent the brightest and most efficient solution processed near-infrared LEDs to date. Here we show that, by concentrating photoexcited states into a small subpopulation of radiative domains, one can achieve a high quantum yield even at low excitation intensities. We tailor the composition of quasi-2D perovskites to direct the energy transfer into the lowest-bandgap minority phase, and to do so faster than it is lost to non-radiative centres. The new material exhibits 60% photoluminescence quantum yield at excitation intensities as low as 1.8 mW/cm2, yielding a ratio of quantum yield to excitation intensity of 0.3 cm2/mW; this represents a two-orders of magnitude decrease in the excitation power required to reach high efficiency compared to the best prior reports. Using this strategy, we report LEDs with EQEs of 7.4% and a high luminescence of 8400 cd/m2.
