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Vacancy-ordered double perovskites (A2BX6) have recently received impressive attention for photovoltaic applications, and the compound K2SnBr6 has desirable features for use in solar cells in such a way that it exhibits direct bandgap behaviour with dispersed band edges. However, the large bandgap value limits its use in higher-efficiency solar cells. Therefore, we have carried out exploratory research by analysing the photovoltaic effect of K2SnBr6 by tuning its bandgap with cation and anion substitutions. We studied the properties of K(2− y)RbySnBr(6− x)I x and K2Sn(1− z)Ti z Br(6− x)I x compounds to explore the photovoltaic effect by gradual substitution of Rb+, Ti4+ and I−1 for K+, Sn4+ and Br−1, respectively. Our density functional calculations in the monoclinic ground state crystal structure with the space group P 121 /n revealed that the K(2− y)Rb y SnBr(6− x)I x compounds considered in this study exhibit direct bandgap behaviour with well-dispersed band edges. Moreover, the bandgap value decreases as a function of the Rb and I concentrations. In addition to the low charge carrier effective mass, low excitonic binding energy values and low recombination rate, these compounds exhibit comparatively greater absorption coefficients in the visible range. The charge carrier transport properties, such as carrier mobility, carrier relaxation time, carrier diffusion coefficient and carrier diffusion length, are also seen in higher ranges for these Rb- and I-substituted compounds when compared to the parent compound. In addition, we have calculated the open-circuit voltage, fill factor, short-circuit current and power conversion efficiency for each compound. From the calculations and analysis, we observed that Rb and I substitution in K2SnBr6 increases the photovoltaic effect, and thus K(2− y)Rb y SnBr(6− x)I x compounds may be employed as absorbing layers in higher-efficiency solar cells. [ABSTRACT FROM AUTHOR]

The study presented here was undertaken to determine the climatic water balance and droughts of Pageru River Basin by using the rainfall data of eight rain gauge stations in and around the Pageru River Basin. The data have been collected and analysed to compute the water balance parameters. The analysis of the data revealed that the annual distribution is mostly controlled by the physiography of the region. A comparison of water balance and cropping pattern adopted in the villages indicates that the area under the basin is only suitable for cultivation of drought-resistant crops, such as jowar, ragi, bajra, etc. [ABSTRACT FROM AUTHOR]

A study was conducted at Pageru river basin, Cuddapah District, Andhra Pradesh, to monitor seasonal fluctuations of groundwater and to determine how the fluctuation in the water levels will affect the groundwater quality. Groundwater levels were found to be influenced by rainfall and pumping of water from the wells for irrigation and domestic uses. Ninety-nine water samples were collected from different wells and analysed for major chemical constituents both in pre- and post-monsoon seasons to determine the quality variation. All major chemical constituents, such as Ca, Mg, Na, K etc., are significantly increased after post-monsoon recharge. According to the overall assessment of the basin, water quality was found to be useful both for drinking and irrigation. [ABSTRACT FROM AUTHOR]