Solution Processed Pbs Quantum Dot Infrared Photodetectors And Photovoltaics Pdf

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Optics Express

However, the epitaxial process used to grow these materials is expensive; therefore, InGaAs-based photodetectors are limited to space exploration and military applications. Along with their cost-efficient solution processability and flexible substrate compatibility, PbS QDs are highly interesting for the quantum-size-effect tunability of their bandgaps, spectral sensitivities, and wide absorption ranges.

In this study, a simple method is proposed to overcome these problems by incorporating CdS in PbS QD shells to provide efficient carrier transfer and enhance the long-term stability of SWIR photodetectors against oxidation.

Semiconductor colloidal quantum dots QDs are promising candidates for next-generation optoelectronic technologies [e. The electrical and optical properties of QDs can be tuned by controlling the size of strong quantum confinement effect [ 10 ]. Among the many applications of QDs, short-wave IR SWIR photodetectors are widely used in bio-imaging, security, face recognition, food safety inspection, and optical communications [ 11 , 12 , 13 , 14 , 15 ].

The technological advancement of SWIR photodetectors is not only attractive for these diverse applications, but also for the commercialization of technologies that are safe for human eyes. The SWIR band is in the range of 1—2. However, the only available high-efficiency photodetector i. Nevertheless, an attractive platform for low-cost photodetectors in the SWIR spectral region is provided by lead sulfide PbS QDs owing to their excellent photosensitivity, bandgap tunability, and solution-processability [ 3 , 18 , 19 , 20 , 21 , 22 ].

In a study by So et al. Gurbuz et al. Hechster et al. Meanwhile, Konstantatos et al. In the simple fabrication method, a layer of QDs was spin-coated onto a pair of preexisting gold electrodes. Although PbS QDs afford good photodetector sensitivity and fast response, they are nevertheless found to be structurally unstable at high temperatures or under severe operating conditions. For practical application in commercial products, QDs are required to have good photo and thermal stabilities.

These properties, along with device performance, have recently been improved by coating an inorganic CdS shell onto a PbS core [ 26 , 27 , 28 ]. Moreover, the type-I structure is not favorable for solar cell and photodetector applications with respect to charge separation and transport. Nevertheless, because the ligand exchange process is performed several times, long processing time can induce binding to the substrate, which acts as a trap and negatively affects photodetector performance [ 33 ].

Therefore, band alignment and interfacial structures have to be engineered to balance charge transfer and surface passivation. According to Jin et al. The gradient interfacial layer between the PbS core and CdS shell allows excitons to partially leak into the shell, which improves the charge transfer.

Improved device performance is demonstrated for an all-solution-processed air-stable SWIR photodetector. The problem of surface passivation is solved by the type-I structure in which a shell of a different wider bandgap semiconductor is grown around the core. To our knowledge, there are previous studies on such self-passivation-based SWIR photodetectors. This lack of studied may exist because the thick shell layer of the type-I structure impedes exciton dissociation, charge extraction, and transport [ 35 ].

The CdS shell generates higher photoluminescence quantum yields PL QYs [ 36 ] and considerably enhances photochemical and thermal stabilities [ 37 ]. By analyzing passivated QDs, we confirmed not only the photostability but also the efficient carrier dynamics and improved lifetime of SWIR photodetectors. To evaluate their performance, we fabricated solution-processable SWIR photodetectors by employing a modification of previously reported methods [ 38 ].

Lead chloride PbCl 2 , All chemicals were used as received, without further purification. PbS QDs were prepared using similar previously reported methods with modifications [ 33 , 38 , 39 ]. In a typical synthesis, 2. Then, ethanol was added; the suspension was centrifuged, and the supernatant was removed. A modification of the sol—gel method was used for the synthesis of ZnO nanoparticles NPs in an alcohol solution [ 7 , 41 , 42 , 43 , 44 , 45 ].

To obtain uniform ZnO NPs, the required aging process was implemented by adding 2-propanol and hexane and allowing the mixture to stand overnight. Then, QDs were spin-coated to form a photoactive layer. Finally, an aluminum Al cathode was deposited via thermal evaporation using a metal shadow mask. According to Pietryga et al. Therefore, the efficiency of cation exchange is closely related to the effective diffusion of ions, which allows to grow thick shells at high temperatures.

Although the total QD size distribution remains similar to that of PbS QDs regardless of the shell thickness, the core becomes non-uniform and more heterogeneous with an increase in shell thickness. Moreover, while excellent core homogeneity and uniform shell thickness are maintained when the shell is relatively thin, a thick shell can result in a core that is heterogeneous in both size and shape owing to the anisotropic nature of the cation exchange approach.

To grow thick shells, the core PbS QD can be stabilized against the Ostwald ripening process at high temperatures [ 36 ]. Two steps of the cation exchange reaction at different temperatures were needed to grow thick shells with a uniform size distribution.

This procedure strongly protects core PbS QDs and enables the high-temperature growth of thick-shell QDs with a uniform size distribution, as confirmed by TEM analysis. The size of PbS QDs is approximately 4. As the CdS surface shell is formed, an effective protective role can be expected; however, it is difficult to induce considerable shell growth by Cd because it has the characteristic of growing by cation exchange between Pb and Cd.

TEM results show that there is no significant difference in particle size; however, there is a large change in optical properties [ 47 ]. Moffitt et al. The characteristics of the synthesized QDs. As shown in Fig. Bulk CdS has a higher peak intensity for reflections compared to reflections, whereas both the PbS QDs and PbS bulk phase have almost equal intensities for these reflections.

The expected increased contribution of the shell layer to the overall composition, relative to that of remaining PbS, is confirmed by the increasing peak intensity and decreasing peak intensity with an increase in the CdS shell thickness.

However, the decreased PbS pattern could not be detected owing to the weak signal from the small core. These results are consistent with those of Zhao et al.

S2 demonstrate a decrease in the Pb ratio along with an increase in the Cd ratio as the thickness of the CdS shell increases. To further understand the passivation provided by the shell material, we measured the time-resolved PL decay, as shown in Fig. As expected, the fastest PL decay was exhibited by PbS QDs owing to the high number of surface defects that feed the non-radiative recombination process [ 39 , 45 , 50 , 51 , 52 ]. The device structure and corresponding energy level diagram are schematically shown in Figs.

Except for the cathode, which was deposited using vacuum thermal evaporation, all other layers were sequentially deposited on the anode by a solution process. The fabrication of multilayered structure requires the use of orthogonal solvents to ensure the integrity of an underlying layer during the deposition of overlayers [ 43 ].

The vertical structure of photodetector provides both a high gain and a quick response owing to its small electrode spacing and a short carrier diffusion pathway.

The fabricated SWIR photodetector functions when incident light is absorbed in the active layer, and photoexcited electron—hole pairs EHPs are drawn to the electrodes by an external electric field. Furthermore, dark current and light current are shown as a function of the applied bias in Additional file 1 : Fig. This measurement allowed us to estimate the signal-to-noise ratio from the dark current, which has been previously shown to considerably contribute to noise [ 53 , 54 ].

Detectivity can be expressed by the following equation:. To demonstrate the photoresponse capability of the device, we measured its response at different applied bias and incident light intensity. Under IR illumination the light current considerably increases, particularly at higher applied voltage, which demonstrates an asymmetrical and non-linear I—V behavior of the photodiode.

The performance of the device under various incident powers from 0. The power of light we used is much weaker than that of a previously reported PbS QD-based photodetector paper. It can be confirmed that the current scale is large in mA, which confirms that the performance of the PbS QD-based photodetector is excellent compared to other reported devices [ 3 , 55 ].

The photoresponse speed provides information on carrier transport in the fabricated device. The current rapidly increased under IR illumination and exponentially decreased without IR illumination. Furthermore, the device exhibited a steady response with repetitive IR illumination. These data indicate that the fabricated device has a very fast response and fall time performance under IR illumination.

In addition, these results indicate that the SWIR PD3 device is more stable under operating conditions and that its lifetime is almost 5. A thicker shell offers the PbS core better protection from the environment along with enhanced photostability. The considerable improvements in electrical performance and stability of the device were attributed to the self-passivation characteristics of the thick CdS shell, which serves as a physical barrier to the penetration of oxygen and moisture.

Sanchez, E. Binetti, J. Torre, G. Garcia-Belmonte, M. Striccoli, I. Nanoscale 6 , — Choi, J. Song, J. Jang, X. Mai, S. Kim, S. Nanoscale 7 , — McDonald, G. Konstantatos, S. Zhang, P. Cyr, E. Klem, L. Levina, E. Sargent, Solution-processed pbs quantum dot infrared photodetectors and photovoltaics. Rauch, M.

Solution-processed PbS quantum dot infrared photodetectors and photovoltaics

However, the epitaxial process used to grow these materials is expensive; therefore, InGaAs-based photodetectors are limited to space exploration and military applications. Along with their cost-efficient solution processability and flexible substrate compatibility, PbS QDs are highly interesting for the quantum-size-effect tunability of their bandgaps, spectral sensitivities, and wide absorption ranges. In this study, a simple method is proposed to overcome these problems by incorporating CdS in PbS QD shells to provide efficient carrier transfer and enhance the long-term stability of SWIR photodetectors against oxidation. Semiconductor colloidal quantum dots QDs are promising candidates for next-generation optoelectronic technologies [e. The electrical and optical properties of QDs can be tuned by controlling the size of strong quantum confinement effect [ 10 ]. Among the many applications of QDs, short-wave IR SWIR photodetectors are widely used in bio-imaging, security, face recognition, food safety inspection, and optical communications [ 11 , 12 , 13 , 14 , 15 ].

Quantum dot

Parcham, E. Introducing nanostructure patterns for performance enhancement in PbS colloidal quantum dot solar cells. International Journal of Nano Dimension , 11 1 , Esmaeil Parcham; Shabnam Andalibi Miandoab.

China E-mail: songhs-wnlo mail.

Supplementary files

Konstantatos icfo. Harnessing low energy photons is of paramount importance for multi-junction high efficiency solar cells as well as for thermo-photovoltaic applications. However, semiconductor absorbers with the bandgap lower than 0. Here, we have developed solution processed low bandgap photovoltaic devices based on PbS colloidal quantum dots CQDs with a bandgap of 0. If you are not the author of this article and you wish to reproduce material from it in a third party non-RSC publication you must formally request permission using Copyright Clearance Center.

Skip to search form Skip to main content You are currently offline. Some features of the site may not work correctly. DOI: McDonald and G. Konstantatos and S.

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4 Comments

  1. Rosemarie C. 25.01.2021 at 22:52

    Solution-processed PbS quantum dot. infrared photodetectors and photovoltaics. STEVEN A. MCDONALD. 1., GERASIMOS KONSTANTATOS.

  2. Finlay G. 27.01.2021 at 07:50

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  3. Cliff R. 27.01.2021 at 08:45

    Quantum dots QDs are semiconductor particles a few nanometres in size, having optical and electronic properties that differ from larger particles due to quantum mechanics.

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