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Incorporation of cesium (Cs) into the perovskite layer has become a good strategy to boost the stability and power conversion efficiency (PCE) of perovskite solar cells (PSCs). However, a suitable and scalable method of Cs incorporation in a perovskite film that does not cause a significant increase in the optical bandgap is needed. In this paper, we introduce a thin layer of CsBr into a formamidinium (FA)-rich mixed halide perovskite film using the thermal evaporation technique. The effects of the thickness of the CsBr layer on the microstructural, structural, and optoelectronic properties and surface chemical states of the perovskite film are then studied. The results indicate that the CsBr layer thickness is able to tune the microstructural and optoelectronic properties of the perovskite film. Planar PSCs fabricated with different thicknesses of CsBr layers in the perovskite absorber exhibited different photovoltaic performance characteristics. The CsBr-modified PSC device with a 50 nm layer of CsBr in the perovskite layer showed a better PCE of 16.19% ± 0.17%, which was about 15% higher than that of the control device, and was able to retain nearly 70% of its initial PCE value after 120 days of storage in an unencapsulated state.

Barite is a non-metallic mineral which is simply barium sulfate (BaSO 4 ) and is largely used by the oil and gas industry as a weighting agent in drilling mud during drilling operations. The specific gravity of barite should range from 4.1 to 4.6 to be applicable as a drilling mud additive. This study considered the occurrence, utilization and challenges facing the mining of barite in Nigeria. It also discussed the global reserve, production and consumption of barite and types of barite ores and associated minerals in Nigeria. With the use of data from various ministries, departments and agencies involved in the records of operations within the Nigerian solid minerals sector, the nature of occurrence of barite in Nigeria has been reviewed. The various reported deposits areas have been elucidated while the associated minerals along with the quality reserve estimates have been discussed. Reported geochemical and geological studies of the barite mineralization in Nigeria show cream to grey, reddish-brown, whitish and pinkish varieties. The quality of the Nigerian barite is moderate to high. It is often associated with dolomite, fluorite, quartz, calcite, etc. The major impurities found in the mineral are iron oxide (goethite), quartz, and carbonates of magnesium, iron and calcium. Enumeration of the challenges facing the exploitation of the mineral has been revealed to include poor infrastructural development, safety and security, insufficient geophysical and geoscience data information and crude mining techniques. The barite production industry still has a huge potential for growth if these challenges are addressed.

In this paper, we use Polyethylene Oxide (PEO) particles to control the morphology of Formamidinium (FA)-rich perovskite films and achieve large grains with improved optoelectronic properties. Consequently, a planar perovskite solar cell (PSC) is fabricated with additions of 5 wt% of PEO, and the highest PCE of 18.03% was obtained. This solar cell is also shown to retain up to 80% of its initial PCE after about 140 h of storage under the ambient conditions (average relative humidity of 62.5 ± 3.25%) in an unencapsulated state. Furthermore, the steady-state PCE of the PEO-modified PSC device remained stable for long (over 2500 s) under continuous illumination. This addition of PEO particles is shown to enable the tuning of the optoelectronic properties of perovskite films, improvements in the overall photophysical properties of PSCs, and an increase in resistance to the degradation of PSCs.

This paper uses a combination of experiments and theory to study the effects of annealing temperature on the mechanical properties of hybrid organic–inorganic perovskites (HOIPs). We examined the mechanical (hardness and Young’s modulus), microstructural, and surface topography properties of the HOIP film at different annealing temperatures ranging from 80 to 170 °C. A mechanism-based strain gradient (MSG) theory is used to explain indentation size effects in films at different annealing temperatures. Intrinsic film yield strengths and hardness values (deduced from the MSG theory) are then shown to exhibit a Hall–Petch dependence on the inverse square root of the average grain size. The implications of the results are then discussed for the design of mechanically robust perovskite solar cells.

The understanding of the degradation mechanisms in perovskite solar cells (PSCs) is important as they tend to degrade faster under exposure to heat and light conditions. This paper examines the temperature-dependent degradation of solution processed triple-cation mixed halide PSCs (Cs0.05(FA0.95MA0.05)0.95Pb(I0.9Br0.05)3). The PSCs were subjected to temperatures between 30 and 60 °C for 3 h (180 min) to evaluate their current–voltage performance characteristics. Temperature-induced changes in the layer and interfacial structure were also elucidated by scanning electron microscopy (SEM). Our results show that thermally induced degradation leads gradually to the burn-in decay of photocurrent density, which results in a rapid reduction in power conversion efficiency. The SEM images reveal thermally induced delamination and microvoid formation between the layers. The underlying degradation in the solar cell performance characteristics is associated with the formation of these defects (interfacial cracks and microvoids) during the controlled heating of the mixed halide perovskite cells. The electrochemical impedance spectroscopy analysis of the PSCs suggests that the device charge transport resistance and the interfacial capacitance associated with charge accumulation at the interfaces both increase with extended exposure to light.

The control of the cation composition of formamidinium (FA), methylammonium (MA), and cesium (Cs) has been used to engineer significant improvements in organic–inorganic perovskite solar cells. However, the thermal stability of mixed-cation perovskite solar cells is not fully understood. In this work, we present the results of an experimental study of the stability of double-cation perovskites [(FAPbI3)0.97(MAPbBr3)0.03] [(FAMA)-perovskite solar cells (PSCs)] and triple-cation based-perovskites [Cs0.05(FA0.95MA0.05)0.95Pb(I0.95Br0.05)3] [(CsFAMA)-PSCs] operated between 40 and 60°C. The thermally induced changes in the film microstructure are elucidated via scanning electron microscopy and x-ray diffraction analyses, and these are related to changes in optoelectronic properties, charge transport, and current–voltage characteristics of (FAMA)-PSCs and (CsFAMA)-PSCs. The implications of the observed degradation mechanisms are also discussed for the future development of efficient and stable PSCs.

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