Fast and reliable DNA sequencing is a long-standing target in biomedical research. Recent advances in graphene-based electrical sensors have demonstrated their unprecedented sensitivity to adsorbed ...molecules, which holds great promise for label-free DNA sequencing technology. To date, the proposed sequencing approaches rely on the ability of graphene electric devices to probe molecular-specific interactions with a graphene surface. Here we experimentally demonstrate the use of graphene field-effect transistors (GFETs) as probes of the presence of a layer of individual DNA nucleobases adsorbed on the graphene surface. We show that GFETs are able to measure distinct coverage-dependent conductance signatures upon adsorption of the four different DNA nucleobases; a result that can be attributed to the formation of an interface dipole field. Comparison between experimental GFET results and synchrotron-based material analysis allowed prediction of the ultimate device sensitivity, and assessment of the feasibility of single nucleobase sensing with graphene.
Back‐contact architectures offer a promising route to improve the record efficiencies of perovskite solar cells (PSCs) by eliminating parasitic light absorption. However, the performance of ...back‐contact PSCs is limited by inadequate carrier diffusion in perovskite. Here, we report that perovskite films with a preferred out‐of‐plane orientation show improved carrier dynamic properties. With the addition of guanidine thiocyanate, the films exhibit carrier lifetimes and mobilities increased by 3–5 times, leading to diffusion lengths exceeding 7 μm. The enhanced carrier diffusion results from substantial suppression of nonradiative recombination and improves charge collection. Devices using such films achieve reproducible efficiencies reaching 11.2 %, among the best performances for back‐contact PSCs. Our findings demonstrate the impact of carrier dynamics on back‐contact PSCs and provide the basis for a new route to high‐performance back‐contact perovskite optoelectronic devices at low cost.
Enhanced charge carrier diffusion in perovskite thin films is demonstrated to significantly improve the efficiency of back‐contact perovskite photovoltaics. The addition of guanidine thiocyanate induces a preferred out‐of‐plane orientation of the perovskite films which exhibit increased carrier diffusion lengths exceeding 7.5 μm. Back‐contact devices using such films display improved efficiencies reaching 11.2 %, a 3‐fold increase in performance.
Metal oxides are the cornerstone of thin‐film electronics, a multibillion dollar industry, because they possess a wide variety of optoelectronic properties, exhibit novel functionalities, and can ...typically be fabricated from cheap, nontoxic raw materials. However, for thin‐film electronics to achieve further market penetration, it is necessary to replace expensive vacuum‐based fabrication processes with low‐cost, large‐scale solution‐based methods. Here, the influence of exposure to air on the band energies of metal oxides is investigated, which is crucial for predicting the operation of thin‐film devices under realistic conditions. A universal reduction in the work function is observed across 18 oxides, and for a subset, n‐type doping of the surfaces is observed after they have been exposed to atmosphere for extended periods of time. These effects arise from charge transfer events with the ubiquitous water layer that forms on surfaces in air. A quantitative analysis of the changes is provided based on the electrochemical transfer doping model, and the amount of transferred charge and the equilibrium work function of oxides in air are calculated which are in agreement with the measurements.
The ubiquitous water layer that forms on surfaces in air is shown to reduce the work function of 18 metal oxides via electrochemical transfer doping. For a subset of five oxides studied, this process is shown to n‐type dope the surface. Detailed modeling reveals that this doping promotes the work function to tend toward 4.7 eV.
The search for lead‐free alternatives to lead‐halide perovskite photovoltaic materials resulted in the discovery of copper(I)‐silver(I)‐bismuth(III) halides exhibiting promising properties for ...optoelectronic applications. The present work demonstrates a solution‐based synthesis of uniform CuxAgBiI4+x thin films and scrutinizes the effects of x on the phase composition, dimensionality, optoelectronic properties, and photovoltaic performance. Formation of pure 3D CuAgBiI5 at x = 1, 2D Cu2AgBiI6 at x = 2, and a mix of the two at 1 < x < 2 is demonstrated. Despite lower structural dimensionality, Cu2AgBiI6 has broader optical absorption with a direct bandgap of 1.89 ± 0.05 eV, a valence band level at ‐5.25 eV, improved carrier lifetime, and higher recombination resistance as compared to CuAgBiI5. These differences are mirrored in the power conversion efficiencies of the CuAgBiI5 and Cu2AgBiI6 solar cells under 1 sun of 1.01 ± 0.06% and 2.39 ± 0.05%, respectively. The latter value is the highest reported for this class of materials owing to the favorable film morphology provided by the hot‐casting method. Future performance improvements might emerge from the optimization of the Cu2AgBiI6 layer thickness to match the carrier diffusion length of ≈40–50 nm. Nonencapsulated Cu2AgBiI6 solar cells display storage stability over 240 days.
Thin films of CuxAgBiI4+x with compositionally controlled phase dimensionality and light‐harvesting properties are synthesized via a simple yet effective hot‐casting method. Using these materials as active layers in thin‐film solar cells enables power‐conversion efficiencies under 1 sun of 2.4% and high environmental stability on a month's timescale.
In this report, a large‐area laser beam induced current microscope that has been adapted to perform intensity modulated photocurrent spectroscopy (IMPS) in an imaging mode is described. ...Microscopy‐based IMPS method provides a spatial resolution of the frequency domain response of the solar cell, allowing correlation of the optoelectronic response with a particular interface, bulk material, specific transport layer, or transport parameter. The system is applied to study degradation effects in back‐contact perovskite cells where it is found to readily differentiate areas based on their markedly different frequency response. Using the diffusion‐recombination model, the IMPS response is modeled for a sandwich structure and extended for the special case of lateral diffusion in a back‐contact cell. In the low‐frequency limit, the model is used to calculate spatial maps of the carrier ambipolar diffusion length. The observed frequency response of IMPS images is then discussed.
A large‐area laser beam induced current microscope adapted to perform intensity modulated photocurrent spectroscopy in an imaging mode is introduced for the first time and applied to study the degradation of a back‐contact perovskite solar cell. Diffusion‐recombination modeling of the spatio‐frequency data allows the extraction of images for key device parameters such as the ambipolar diffusion length.
In this work, we describe the formation of a reduced bandgap CeNiO3 phase, which, to our knowledge, has not been previously reported, and we show how it is utilized as an absorber layer in a ...photovoltaic cell. The CeNiO3 phase is prepared by a combinatorial materials science approach, where a library containing a continuous compositional spread of Ce x Ni1–x O y is formed by pulsed laser deposition (PLD); a method that has not been used in the past to form Ce–Ni–O materials. The library displays a reduced bandgap throughout, calculated to be 1.48–1.77 eV, compared to the starting materials, CeO2 and NiO, which each have a bandgap of ∼3.3 eV. The materials library is further analyzed by X-ray diffraction to determine a new crystalline phase. By searching and comparing to the Materials Project database, the reduced bandgap CeNiO3 phase is realized. The CeNiO3 reduced bandgap phase is implemented as the absorber layer in a solar cell and photovoltages up to 550 mV are achieved. The solar cells are also measured by surface photovoltage spectroscopy, which shows that the source of the photovoltaic activity is the reduced bandgap CeNiO3 phase, making it a viable material for solar energy.
Data mining tools have been known to be useful for analyzing large material data sets generated by high-throughput methods. Typically, the descriptors used for the analysis are structural ...descriptors, which can be difficult to obtain and to tune according to the results of the analysis. In this Research Article, we show the use of deposition process parameters as descriptors for analysis of a photovoltaics data set. To create a data set, solar cell libraries were fabricated using iron oxide as the absorber layer deposited using different deposition parameters, and the photovoltaic performance was measured. The data was then used to build models using genetic programing and stepwise regression. These models showed which deposition parameters should be used to get photovoltaic cells with higher performance. The iron oxide library fabricated based on the model predictions showed a higher performance than any of the previous libraries, which demonstrates that deposition process parameters can be used to model photovoltaic performance and lead to higher performing cells. This is a promising technique toward using data mining tools for discovery and fabrication of high performance photovoltaic materials.
In this work, we describe the formation of a reduced bandgap CeNiO
phase, which, to our knowledge, has not been previously reported, and we show how it is utilized as an absorber layer in a ...photovoltaic cell. The CeNiO
phase is prepared by a combinatorial materials science approach, where a library containing a continuous compositional spread of Ce
Ni
O
is formed by pulsed laser deposition (PLD); a method that has not been used in the past to form Ce-Ni-O materials. The library displays a reduced bandgap throughout, calculated to be 1.48-1.77 eV, compared to the starting materials, CeO
and NiO, which each have a bandgap of ∼3.3 eV. The materials library is further analyzed by X-ray diffraction to determine a new crystalline phase. By searching and comparing to the Materials Project database, the reduced bandgap CeNiO
phase is realized. The CeNiO
reduced bandgap phase is implemented as the absorber layer in a solar cell and photovoltages up to 550 mV are achieved. The solar cells are also measured by surface photovoltage spectroscopy, which shows that the source of the photovoltaic activity is the reduced bandgap CeNiO
phase, making it a viable material for solar energy.
Back‐contact architectures offer a promising route to improve the record efficiencies of perovskite solar cells (PSCs) by eliminating parasitic light absorption. However, the performance of ...back‐contact PSCs is limited by inadequate carrier diffusion in perovskite. Here, we report that perovskite films with a preferred out‐of‐plane orientation show improved carrier dynamic properties. With the addition of guanidine thiocyanate, the films exhibit carrier lifetimes and mobilities increased by 3–5 times, leading to diffusion lengths exceeding 7 μm. The enhanced carrier diffusion results from substantial suppression of nonradiative recombination and improves charge collection. Devices using such films achieve reproducible efficiencies reaching 11.2 %, among the best performances for back‐contact PSCs. Our findings demonstrate the impact of carrier dynamics on back‐contact PSCs and provide the basis for a new route to high‐performance back‐contact perovskite optoelectronic devices at low cost.
Enhanced charge carrier diffusion in perovskite thin films is demonstrated to significantly improve the efficiency of back‐contact perovskite photovoltaics. The addition of guanidine thiocyanate induces a preferred out‐of‐plane orientation of the perovskite films which exhibit increased carrier diffusion lengths exceeding 7.5 μm. Back‐contact devices using such films display improved efficiencies reaching 11.2 %, a 3‐fold increase in performance.
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