The photovoltaics of organic–inorganic lead halide perovskite materials have shown rapid improvements in solar cell performance, surpassing the top efficiency of semiconductor compounds such as CdTe and CIGS (copper indium gallium selenide) used in solar cells in just about a decade. Perovskite preparation via simple and inexpensive solution processes demonstrates the immense potential of this thin-film solar cell technology to become a low-cost alternative to the presently commercially available photovoltaic technologies. Significant developments in almost all aspects of perovskite solar cells and discoveries of some fascinating properties of such hybrid perovskites have been made recently. This Review describes the fundamentals, recent research progress, present status, and our views on future prospects of perovskite-based photovoltaics, with discussions focused on strategies to improve both intrinsic and extrinsic (environmental) stabilities of high-efficiency devices. Strategies and challenges regardi...

Halide Perovskite Photovoltaics: Background, Status, and Future Prospects

Current-density-voltage (J-V) hysteresis in perovskite solar cells (PSCs) is a critical issue because it is related to power conversion efficiency and stability. Although parameters affecting the hysteresis have been already reported and reviewed, little investigation is reported on scan-direction-dependent J-V curves depending on perovskite composition. This review investigates J-V hysteric behaviors depending on perovskite composition in normal mesoscopic and planar structure. In addition, methodologies toward hysteresis-free PSCs are proposed. There is a specific trend in hysteresis in terms of J-V curve shape depending on composition. Ion migration combined with nonradiative recombination near interfaces plays a critical role in generating hysteresis. Interfacial engineering is found to be an effective method to reduce the hysteresis; however, bulk defect engineering is the most promising method to remove the hysteresis. Among the studied methods, KI doping is proved to be a universal approach toward hysteresis-free PSCs regardless of perovskite composition. It is proposed from the current studies that engineering of perovskite film near the electron transporting layer (ETL) and the hole transporting layer (HTL) is of vital importance for achieving hysteresis-free PSCs and extremely high efficiency.

On the Current-Voltage Hysteresis in Perovskite Solar Cells: Dependence on Perovskite Composition and Methods to Remove Hysteresis

Recent success in achieving highly stable Rb-containing organolead halide perovskites has indicated the possibility of incorporating small monovalent cations, which cannot fit in the lead-halide cage with an appropriate tolerance factor, into the perovskite lattice while maintaining a pure stable "black" phase. In this study, through a combined experimental and theoretical investigation by density functional theory (DFT) calculations on the incorporation of extrinsic alkali cations (Rb+ , K+ , Na+ , and Li+ ) in perovskite materials, the size-dependent interstitial occupancy of these cations in the perovskite lattice is unambiguously revealed. Interestingly, DFT calculations predict the increased ion migration barriers in the lattice after the interstitial occupancy. To verify this prediction, ion migration behavior is characterized through hysteresis analysis of solar cells, electrical poling, temperature-dependent conductivity, and time-dependent photoluminescence measurements. The results collectively point to the suppression of ion migration after lattice interstitial occupancy by extrinsic alkali cations. The findings of this study provide new material design principles to manipulate the structural and ionic properties of multication perovskite materials.

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Interstitial Occupancy by Extrinsic Alkali Cations in Perovskites and Its Impact on Ion Migration.

Solution-Processed All-Perovskite Multi-junction Solar Cells

Nitrogen Fixing Organisms: Pure and Applied Aspects

Amorphous to crystalline phase transformation and band gap refinement in ZnSe thin films

In this article, we have demonstrated the doping of K in the light absorbing CH 3 NH 3 PbI 3 perovskite i.e. (M = CH 3 , A = NH 3 ; x = 0–1). One of the major merits of methylammonium lead iodide (CH 3 NH 3 PbI 3 ) perovskites is that they act as efficient absorbing material of light in photovoltaic cell imparting long carrier lifetime and optimum band gap. The structural, morphological, electronic and optoelectric properties of potassium (K) doped light absorber methylammonium lead iodide (CH 3 NH 3 PbI 3 ) perovskites are reported here i.e. K x (MA) 1−x PbI 3 (M = CH 3 , A =NH 3; x = 0–1). The thin films of perovskites (x = 0–1) were deposited by spin coating on cleaned FTO substrates and characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM), current-voltage (IV), X-ray photoelectron spectroscopy (XPS) and Diffused reflectance spectroscopy (DRS) analysis. The organic constituents i.e. MA = CH 3 NH 3 , in perovskites solar cells induce instability even at the room temperature. To overcome such instabilities we have replaced the organic constituents by K because both of them have electropositive nature. Potassium successfully replaces the CH 3 NH 3 . Initially, this compound grows in a tetragonal crystal structure, however, beyond 30% doping of potassium orthorhombic distortions are induced in the parent tetragonal unit cell. Such phase transformation is microscopically visible in the electron micrographs of doped samples; cubic grains for MAPbI 3 begin to transform into strip like structures in K-doped samples. The resistance of the samples is decreased for partial K-doping, which we suggested to be arising due to the electropositive nature of K. It is observed that the binding energy difference between Pb4f and I3d core levels are very similar in all the investigated systems and show formal oxidation states. Also, the partially doped samples showed increased absorption and bandgaps around 1.5 eV which is an optimum value for solar absorption.

Potassium doped methylammonium lead iodide (MAPbI 3 ) thin films as a potential absorber for perovskite solar cells; structural, morphological, electronic and optoelectric properties

Synthesis and characterization of (CuO)
 x
 /Cu0.5Tl0.5Ba2Ca2Cu3O10−δ
 ; {(CuO)
 x
 /CuTl-1223} composites with x=0 %, 10 %, 15 % and 20 % have been reported. The fluctuations induced conductivity (FIC) analysis of (CuO)
 x
 /CuTl-1223 composite has been carried out using Aslamazov-Larkin (AL) and Lawrence-Doniach (LD) models in the temperature regime well above the critical temperature (T>T
 c
 ). The electrical resistivity versus temperature curves of as-prepared and oxygen post-annealed (CuO)
 x
 /CuTl-1223 composite were fitted by using above mentioned models to extract the microscopic parameters such as zero temperature coherence length along c-axis{ξ
 c
 (0)}, inter-layer coupling (J), dimensional critical exponent (λ) and inter-grain coupling constant (α) etc. It has been observed that the cross-over temperature (T
 o
 ) fits very well the two-dimensional (2D) and three-dimensional (3D) AL equations and shifts towards the lower temperature regime with the enhanced weight percentage of CuO nano-particles. The shifting of AL 3D region to higher temperature after oxygen post-annealing indicates the restoration of oxygen and optimization of charge carriers in conducting CuO2 planes. The gradual decrease in the value of inter-grain coupling constant (α) with the increase of CuO nano-particles content reflects an improvement in the inter-grain coupling resulting into an increase in the coherence length (ξ
 c
 ) along the c-axis. Almost all superconductivity parameters have been improved after oxygen post-annealing. The suppression of superconductivity parameters in the composite with x=20 % limits the optimum doping level of CuO nano-particles in (CuO)
 x
 /CuTl-1223 composite.

Study of CuO Nano-particles/CuTl-1223 Superconductor Composite

Polycrystalline (Cu0.5Tl0.5)Ba2Ca2Cu3O10−δ superconductors show strong composition variations at the termination ends of the crystals which compromise over-all superconducting properties of the final compound. These composition variations are one of the root causes of void formation which produces a poor quality material. The better inter-grain coupling suppresses the Josephson losses required for higher transport critical current density (J c ). The lower losses across the inter-grain Josephson junctions are essential for wire and microelectronic applications. We have fixed such inadvertent composition variation in (Cu0.5Tl0.5)Ba2Ca2Cu3O10−δ superconductors by doping them with nano-particles of CuO, BaO and CaO2. Nano-particles doped (Cu0.5Tl0.5)Ba2Ca2Cu3O10−δ superconductors were synthesized at 860 °C and characterized using X-ray diffraction (XRD), resistivity (ρ), ac-susceptibility (χ), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) measurements. The magnitude of superconductivity is significantly enhanced with the doping of nano-particles. The samples with 15 wt. % addition of CuO nano-particles have even shown textured elongated crystalline with extremely low population of voids.

Enhanced Inter-grain Connectivity in Nano-particles Doped (Cu0.5Tl0.5)Ba2Ca2Cu3O10−δ Superconductors

In this work, we have investigated the (MA)1−xCsxPbI3(MA = CH3NH3; x = 0–1) perovskite based solar cells. The x-ray diffraction analysis revealed that crystal structure of the material has been transformed from tetragonal to orthorhombic phase with Cs doping. The optical spectra are blue shifted with Cs doping, suggesting the increase in the band gap and this effect is more prominent in higher Cs doping. From x-ray photoemission spectroscopy analysis, binding energy difference between Pb and I doublets is observed to be fixed. The oxygen and carbon peaks responsible for decomposition of MAPbI3 decreases in intensity in partial doped sample, showing the stability of the material by introducing oxidation stable Cs. The power conversion efficiency (PCE) was investigated and the best performing device with PCE of 15.37% was achieved with 30% Cs doping, with open circuit voltage of 1.08 V, current density of 19.70 mA/cm2, and fill factor of 0.72.

Enhanced efficiency and stability of perovskite solar cells by partial replacement of CH3NH3+ with inorganic Cs+ in CH3NH3PbI3 perovskite absorber layer

Abida Saleem

Papers

Amorphous to crystalline phase transformation and band gap refinement in ZnSe thin films

Potassium doped methylammonium lead iodide (MAPbI 3 ) thin films as a potential absorber for perovskite solar cells; structural, morphological, electronic and optoelectric properties

Study of CuO Nano-particles/CuTl-1223 Superconductor Composite

Enhanced Inter-grain Connectivity in Nano-particles Doped (Cu0.5Tl0.5)Ba2Ca2Cu3O10−δ Superconductors

Enhanced efficiency and stability of perovskite solar cells by partial replacement of CH3NH3+ with inorganic Cs+ in CH3NH3PbI3 perovskite absorber layer