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In this work, we propose and demonstrate a carbon nanotube (CNT) field-effect transistor (FET) based biosensor for selective detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). CNT FETs were fabricated on a flexible Kapton substrate and the sensor was fabricated by immobilizing the reverse sequence of the 25-base portion of the RNA-dependent RNA polymerase gene of the SARS-CoV-2 onto the CNT channel. The biosensors were tested for the synthetic positive and control target sequences. The biosensor showed a selective sensing response to the positive target sequence with a limit of detection of 10 fM. The promising results from our study suggest that the CNT FET based biosensors can be used as a diagnostic tool for the detection of SARS-CoV-2.

This study focuses on the fabrication and characterization of Cs2AgBiBr6 double perovskite thin film for field-effect transistor (FET) applications. The Cs2AgBiBr6 thin films were fabricated using a solution process technique and the observed XRD patterns demonstrate no diffraction peaks of secondary phases, which confirms the phase-pure crystalline nature. The average grain sizes of the spin-deposited film were also calculated by analysing the statistics of grain size in SEM image and was found to be around 412 (±44) nm the larger grain size was also confirmed by the XRD measurements. FETs with different channel lengths of Cs2AgBiBr6 thin films were fabricated on an electrode deposited heavily doped p-type Si substrate with a 300 nm thermally grown SiO2 dielectric under ideal conditions in air processing under ambient pressure and temperature. The Cs2AgBiBr6 FETs showed a p-type nature with a positive threshold voltage. The on current, threshold voltage and hole-mobility of the FETs decreased with increasing channel length. A high average hole mobility of 0.29 cm2s-1V-1 was obtained for the FETs with a channel length of 30 µm, and the hole mobility was reduced by an order of magnitude (0.012 cm2s-1V-1) when the channel length was doubled. The on current and hole-mobility of Cs2AgBiBr6 FETs followed a power fit, which confirmed the dominance of channel length in electrostatic gating in Cs2AgBiBr6 FETs. A very high-hole mobility observed in or FET that could be attributed to the much larger grain size of Cs2AgBiBr6 film made in this work.

This study focuses on employing cuprous iodide (CuI) as a hole-transporting material (HTM) in fabricating highly efficient perovskite solar cells (PSCs). The PSCs were made in air with either CuI or 2,2&prime, 7,7&prime, Tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9&prime, spirobifluorene (spiro-OMeTAD) as HTMs. A simple and novel pressing method was employed for incorporating CuI powder layer between perovskite layer and Pt top-contact to fabricate devices with CuI, while spiro-OMeTAD was spin-coated between perovskite layer and thermally evaporated Au top-contact to fabricate devices with spiro-OMeTAD. Under illuminations of 100 mW/cm2 with an air mass (AM) 1.5 filter in air, the average short-circuit current density (JSC) of the CuI devices was over 24 mA/cm2, which is marginally higher than that of spiro-OMeTAD devices. Higher JSC of the CuI devices can be attributed to high hole-mobility of CuI that minimizes the electron-hole recombination. However, the average power conversion efficiency (PCE) of the CuI devices were lower than that of spiro-OMeTAD devices due to slightly lower open-circuit voltage (VOC) and fill factor (FF). This is probably due to surface roughness of CuI powder. However, optimized devices with solvent-free powder pressed CuI as HTM show a promising efficiency of over 8.0 % under illuminations of 1 sun (100 mW/cm2) with an air mass 1.5 filter in air, which is the highest among the reported efficiency values for PSCs fabricated in an open environment with CuI as HTM.

In this work, chemical bath-deposited cadmium sulfide (CdS) thin films were employed as an alternative hole-blocking layer for inverted poly(3-hexylthiophene) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM) bulk heterojunction solar cells. CdS films were deposited by chemical bath deposition and their thicknesses were successfully controlled by tailoring the deposition time. The influence of the CdS layer thickness on the performance of P3HT:PCBM solar cells was systematically studied. The short circuit current densities and power conversion efficiencies of P3HT:PCBM solar cells strongly increased until the thickness of the CdS layer was increased to ~70 nm. This was attributed to the suppression of the interfacial charge recombination by the CdS layer, which is consistent with the lower dark current found with the increased CdS layer thickness. A further increase of the CdS layer thickness resulted in a lower short circuit current density due to strong absorption of the CdS layer as evidenced by UV-Vis optical studies. Both the fill factor and open circuit voltage of the solar cells with a CdS layer thickness less than ~50 nm were comparatively lower, and this could be attributed to the effect of pin holes in the CdS film, which reduces the series resistance and increases the charge recombination. Under AM 1.5 illumination (100 mW/cm2) conditions, the optimized PCBM:P3HT solar cells with a chemical bath deposited a CdS layer of thickness 70 nm and showed 50% power conversion efficiency enhancement, in comparison with similar solar cells with optimized dense TiO2 of 50 nm thickness prepared by spray pyrolysis.

Self-assembled monolayers (SAMs) of benzoic acid based molecules are used to modify the metal oxide–polymer interface in a hybrid poly-3-hexylthiophene (P3HT)/TiO2 photovoltaic device structure. The effect of SAMs on current density is in accordance with expectation from the driving force for charge separation of metal oxide–polymer interface in a hybrid poly-3-hexylthiophene (P3HT)/TiO2 photovoltaic device. However, the effect of monolayers on open circuit voltage is quite unexpected from the interfacial energetics as all the monolayers improve the open circuit voltage in spite of different sign of the interfacial dipole for different SAMs. This suggests that the monolayers have additional functions. Overall device performance is enhanced by more than a factor of two using a SAM with permanent dipole pointing towards the TiO2 surface or pointing towards polymer when compared to a control device with no interface modifiers. This study concludes that the SAM layer has two functions that are to shift the position of the conduction band of the porous TiO2 relative to the polymer HOMO level so as to influence interfacial charge separation and to act as a barrier layer, insulating back electron transfer from the TiO2 to the polymer. Both effects can benefit the performance of hybrid polymer metal oxide solar cells.

This work focused on studying the effect of cadmium sulfide (CdS) interfacial layer on the performance of titanium dioxide (TiO2)/poly (3-hexylthiophene) (P3HT) solar cells and finding out its effect on charge recombination dynamics of hybrid TiO2/P3HT solar cells. FESEM images confirm the uniform distribution of chemical bath deposited CdS layer on TiO2 nanoparticles. Insertion of CdS layer at the nanocrystalline TiO2/P3HT interface broadens quantum efficiency spectrum of the solar cells with peak values over 80 and 40 % at the wavelengths of maximum absorption of CdS and P3HT respectively and hence enhances short-circuit current density (JSC) from 3.5 to 5.9 mAcm−2 under simulated illumination (70 mWcm−2) with an AM 1.5 filter. CdS layer further improves open circuit voltage (VOC) from 0.35 to 0.57 V, which is consistent with higher built-in voltage in CdS/P3HT than in TiO2/P3HT due to relatively lower laying conduction band edge of CdS. Photovoltaic transient measurements show that the carrier life-time in TiO2/CdS/P3HT solar cell is an order of magnitude longer than that in TiO2/P3HT solar cell. Optimized TiO2/P3HT solar cells with CdS interlayer yield power conversion efficiencies over 1.5 %, which is three times greater than that for similar solar cells without CdS layer.

In this work, alternative architecture for polymer/fullerene solar cells has been explored using titanium dioxide nanolayers which invert the polarity of the cell and may relax the necessity to have a hole-collecting buffer layer poly(styrene sulfonate)-doped poly(ethylene dioxy-thiophene) (PEDOT:PSS). This work particularly focuses on the performance of the inverted devices with dense TiO 2 nanolayers as a function of temperature, illumination intensity and time. We find that both temperature and illumination intensity slightly influence the power conversion efficiency of devices with the PEDOT:PSS layer. However, the inverted solar cells without the PEDOT:PSS layer showed very different characteristics regarding the power conversion efficiency which increased significantly with the operating temperature from 30 °C to 65 °C. This was attributed to a consequence from the strong and positive temperature dependence of open-circuit voltage which may be due to a "kink" in the current―voltage characteristics near the open-circuit voltage.

We report a study of the effects of polymer optoelectronic properties on the performance of photovoltaic devices consisting of nanocrystalline TiO2 and a conjugated polymer. Three different poly(2-methoxy-5-(2′-ethylhexoxy)-1,4-phenylenevinylene) (MEH-PPV)-based polymers and a fluorene–bithiophene copolymer are compared. We use photoluminescence quenching, time-of-flight mobility measurements, and optical spectroscopy to characterize the exciton-transport, charge-transport, and light-harvesting properties, respectively, of the polymers, and correlate these material properties with photovoltaic-device performance. We find that photocurrent is primarily limited by the photogeneration rate and by the quality of the interfaces, rather than by hole transport in the polymer. We have also studied the photovoltaic performance of these TiO2/polymer devices as a function of the fabrication route and device design. Including a dip-coating step before spin-coating the polymer leads to excellent polymer penetration into highly structured TiO2 networks, as was confirmed through transient optical measurements of the photoinduced charge-transfer yield and recombination kinetics. Device performance is further improved for all material combinations studied, by introducing a layer of poly(ethylene dioxythiophene) (PEDOT) doped with poly(styrene sulfonic acid) (PSS) under the top contact. Optimized devices incorporating the additional dip-coated and PEDOT:PSS layers produced a short-circuit current density of about 1 mA cm–2, a fill factor of 0.50, and an open-circuit voltage of 0.86 V under simulated AM 1.5 illumination (100 mW cm–2, 1 sun). The corresponding power conversion efficiency under 1 sun was ≥ 0.4 %.

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We report on a study of post-processing treatments in hybrid solar cells based on poly(3-hexylthiophene) (P3HT) being in contact with nanocrystalline TiO2 films. The power conversion efficiency of the hybrid polymer/TiO2 solar cells is increased over three-fold through the simultaneous application of external bias voltage and UV illumination. These treatments enhance short-circuit current density, J(SC), from 1 mA/cm(2) to over 3 mA/cm(2) under simulated air mass (AM) 1.5 conditions (100 mW cm(-2)) and lead to a peak external quantum efficiency of over 16%. The AM 1.5 open circuit voltage reaches 0.47 V and the fill factor reaches 0.53, resulting in an overall power conversion efficiency of 0.74%. The improved performance following UV exposure is correlated to a slowing of over one order of magnitude in the dynamics of charge recombination as monitored by transient optical spectroscopy. We further demonstrate that while the UV radiation present in a simulated AM 1.5 solar spectrum is sufficient to cause the increase in the J(SC) and efficiency after two hours of exposure, no change results from exposure to the same spectrum when a UV blocking filter is used. We propose that UV exposure modifies the nature or density of surface trapping species in the nanocrystalline TiO2, resulting in reduced recombination rates and a higher efficiency of collection of photogenerated charges., The authors thank Prof. James Durrant, Department of Chemistry, Imperial College London, for permitting them to take transient absorption spectroscopic measurements in his laboratory. PR and JN thank the Royal Society for financial support of PR's academic visit to Imperial College London. We also thank the EPSRC Excitonic Supergen Programme (EP/G031088) and the EPSRC Materials for Energy Programme (EP/E036341/1) for financial support. PA acknowledges the support of the Spanish Ministry of Science for a post-doctoral fellowship.

We report on the effect of nanoparticle morphology and interfacial modification on the performance of hybrid polymer/zinc oxide photovoltaic devices. We compare structures consisting of poly-3-hexylthiophene (P3HT) polymer in contact with three different types of ZnO layer: a flat ZnO backing layer alone; vertically aligned ZnO nanorods on a ZnO backing layer; and ZnO nanoparticles on a ZnO backing layer. We use scanning electron microscopy, steady state and transient absorption spectroscopies, and photovoltaic device measurements to study the morphology, charge separation, recombination behavior and device performance of the three types of structures. We find that charge recombination in the structures containing vertically aligned ZnO nanorods is remarkably slow, with a half-life of several milliseconds, over 2 orders of magnitude slower than that for randomly oriented ZnO nanoparticles. A photovoltaic device based on the nanorod structure that has been treated with an amphiphilic dye before deposition of the P3HT polymer yields a power conversion efficiency over four times greater than that for a similar device based on the nanoparticle structure. The best ZnO nanorod:P3HT device yields a short circuit current density of 2 mAcm(-2) under AM1.5 illumination (100 mW cm(-2)) and a peak external quantum efficiency over 14%, resulting in a power conversion efficiency of 0.20%.

This study focuses on systems consisting of high hole-mobility MEHPPV based polymers or a fluorene-bithiophene co-polymer in contact with different nanocrystalline TiO 2 films. We use photoluminescence quenching, time of flight mobility measurements and optical spectroscopy to characterize the exciton transport, charge transport and light harvesting properties, respectively, of the polymers, and correlate these material properties with photovoltaic device performance. We find that the polymer properties with greatest influence on device efficiency are the polymer exciton diffusion length and absorption range, followed by the hole mobility. We have also studied the photovoltaic performance of these TiO 2 /polymer devices as a function of active layer thickness. Device performances are significantly improved by introducing a PEDOT layer between the polymer and the top Au electrode and by reducing the thickness of the active layers. The optimized devices have peak external quantum efficiencies ≃ 40 % at the polymer's maximum absorption wavelength and yield short circuit current densities ≥ 2 mA cm -2 for air mass (AM) 1.5 conditions (100 mW cm -2 , 1 sun). The AM 1.5 open circuit voltage reaches 0.64 V and the fill factor 0.43, resulting in an overall power conversion efficiency of 0.58 %.

We study the charge recombination kinetics and photovoltaic performance of composites of poly (9,9-dioctylfluorene-co-bithiophene) polymer with nanocrystalline TiO 2 . Transient optical spectroscopy confirms that photoexcitation of the polymer leads to electron transfer to the TiO 2 and indicates that charge recombination is slow with a half-time of 100 μs to 10ms. Polymer penetration into thick porous TiO 2 layers is improved by melt-processing and treatment of the TiO 2 surface. We study the photovoltaic characteristics of devices with different layer thickness and interface morphology. Quantum efficiency (QE) of all devices is increased by reducing the TiO 2 and polymer layer thickness. Inserting a thin porous TiO 2 layer in to a thin bi-layer device increases the QE by a factor of five. The improved device shows peak QE and monochromatic power conversion efficiencies of over 11% and 1% at 440nm respectively. The device produced a short-circuit current density of 300μAcm -2 , a fill factor of 0.24 and an open-circuit voltage of 0.8V under AM1.5 illumination. The fill factor is increased from 0.24 to 0.40 by introducing an additional dip-coating layer and overall power conversion efficiency is increased by 50%. However, the device produced degraded current-voltage characteristics. We investigate this using an alternative polymers and different top contact metals.

We focus on the preparation of hybrid polymer/zinc oxide (ZnO) solar cells, in which the metal oxide consists of ZnO columnar structures grown perpendicularly on a flat, dense “backing” layer, as a means to provide a direct and ordered path for photogenerated electrons to the collecting electrode. We used scanning electron microscopy, absorption spectroscopy and photovoltaic device measurements to study the morphology and device performance of the prepared structures. Different solution chemical routes were investigated for the synthesis of the inorganic device components, i.e. the ZnO columnar structures and the “backing” layers, which act as a seed-growth layer for the ZnO rods. The growth of the ZnO rods was dependent on the morphological and structural characteristics of the seed layer and moreover, the seed layer itself was also affected by the synthetic conditions for ZnO rod growth. Different polymers (high hole-mobility MEH-PPV based polymer and P3HT) were compared in these structures and power conversion efficiencies of 0.15 and 0.20% were achieved under 1 Sun illumination, respectively. Results are discussed in terms of the optoelectronic properties of the polymers.

We report a study of the optimization of power conversion efficiency in hybrid solar cells based on nanostructured titanium dioxide and a poly[2-(2-ethylhexyloxy)-5-methoxy-1,4-phenylenevinylene] (MEH-PPV) based conjugated polymer. Charge collection efficiency is enhanced by introducing a poly(ethylenedioxythiophene)/polystyrene sulphonate (PEDOT) layer (under the gold electrode) as the hole collector. Device performance is maximized for a device with a net active layer thickness of 100 nm. The optimized device has peak external quantum efficiencies ≈40% at the polymer’s maximum absorption wavelength and yield short circuit current density ⩾2mAcm−2 for air mass (AM) 1.5 conditions (100mWcm−2, 1 sun). The AM 1.5 open circuit voltage for this device is 0.64 V and the fill factor is 0.43, resulting in an overall power conversion efficiency of 0.58%.