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DNA nanoswitches can be designed to detect unlabelled nucleic acid targets and have been shown to discriminate between targets which differ in the identity of only one base. This paper demonstrates that the fluorescent base analogue 2-aminopurine (AP) can be used to discriminate between nanoswitches with and without targets and to discriminate between matched and mismatched targets. In particular, we have used both steady-state and time-resolved fluorescence spectroscopy to determine differences in AP environment at the branchpoint of nanoswitches assembled using complementary targets and targets which incorporate single base mismatches. [ABSTRACT FROM AUTHOR]

Kesterite solar cells based on chalcogenide Cu2ZnSn(S,Se)4 (CZTSSe) are a viable approach to thin film photovoltaics, utilising Earth-abundant, non-toxic elements. CZTSSe films produced from nanoparticle inks offer a cost-effective solution-based method of fabrication. However, improving efficiency in these devices has proved challenging, in part due to the presence of detrimental complex defects within the bulk of the CZTSSe absorber. In this study, the behaviour of nanoparticle-based CZTSSe absorbers and solar cells made from relatively low and high quality grade chemicals is investigated with a view to improving cost-effectiveness of the ink-based fabrication process. Photoluminescence spectroscopy revealed the presence of similar shallow acceptor plus shallow donor states in both low and high purity precursor absorbers. We demonstrate a relationship between the average depth of energy band-edge potential fluctuations and absorber quality where the higher grade chemical precursor-based absorber outperforms the lower purity version. In addition, the low purity precursor absorber had a higher total defect density resulting in a 10 meV increase in the average electrostatic potential fluctuations. Deep level transient spectroscopy in solar devices indicated the presence of detrimental deep defect states in both types of absorber. Notwithstanding the high purity precursor absorber with lower defect density, the power conversion efficiencies of both types of CZTSSe solar cells were similar (∼5%), implying an issue other than defects in the absorber bulk inhibits device performance as evidenced by quantum efficiency analysis and current–voltage measurements. [ABSTRACT FROM AUTHOR]

Cu2ZnSn(S,Se)4 (CZTSSe) thin film photovoltaic absorber layers are fabricated by selenizing Cu2ZnSnS4 (CZTS) nanoparticle thin films in a selenium rich atmosphere. The selenium vapor pressure is controlled to optimize the morphology and quality of the CZTSSe thin film. The largest grains are formed at the highest selenium vapor pressure of 226 mbar. Integrating this photovoltaic absorber layer in a conventional thin film solar cell structure yields a champion short circuit current of 37.9 mA/cm2 without an antireflection coating. This stems from an improved external quantum efficiency characteristic in the visible and near-infrared part of the solar spectrum. The physical basis of this improvement is qualitatively attributed to a substantial increase in the minority carrier diffusion length. [ABSTRACT FROM AUTHOR]

Tin sulphide (SnS) thin films deposited by thermal evaporation on glass substrates are studied for different substrate temperatures. The increase in substrate temperature results in the increase of the crystallite size and change in orientation of the films. The crystal structure of the films is that of SnS only and for temperatures ≤300 °C the films are of random orientation, whereas for higher temperatures the films become (040) oriented. The variation of Sn/S composition was accompanied by a reduction in optical energy bandgap from 1.47 to 1.31 eV as the substrate temperature increases. The Urbach energy was found stable at 0.169 ± 0.002 eV for temperature up to 350 °C. Photoluminescence emission was observed only for films exhibiting stoichiometric properties and shows that a precise control of the film composition is critical to fabricate devices while an increase in grain size will be essential to achieve high efficiency. [ABSTRACT FROM AUTHOR]