Mixed-Cation Mixed-Metal Halide Perovskites for Photovoltaic Applications: A Theoretical Study

Ga and In-based hybrid halide perovskites as an alternative to Pb: a first principles study

Lead-free hybrid halide perovskites have gained much attention in the field of photovoltaics due to their non-toxicity, stability and unique photo-physical properties. Sn and Ge-based ABX3 perovskites have been widely studied due to their similar electronic properties to Pb-based materials. However, the unstable oxidation state of Sn is a major challenge for the commercialization of this class of materials. To overcome this problem, here, we have designed a series of novel Ga and In-based A3B2X9-type perovskite materials incorporating the methylammonium (MA) organic cation in the A site and I- as the halide ion in the X site. In this regard, we have investigated different structural, electronic, optical and photovoltaic properties by employing the density functional theory formalism. The formation of a stable three dimensional perovskite structure is determined by the observed values of tolerance factor (TF) and octahedral factor (μ). The observed negative values of formation enthalpy manifest that our studied materials are also thermodynamically stable. The obtained band gap values reveal that our designed perovskite materials can act as semiconducting materials for application in photovoltaics. We have also investigated the optical properties of our studied materials and the observed values of dielectric function and absorption coefficient in the visible range of the electromagnetic spectrum indicate their excellent photo absorption. The observed theoretical power conversion efficiency (PCE) values reveal that (MA)3In2I9 (13.82%) and (MA)3 (Ga.50In.50)2I9 (12.8%) can be chosen as potential candidates for application in perovskite-based photovoltaics. This research provides a pathway for the development of less toxic and efficient semiconducting materials, offering exciting prospects for their utilization in optoelectronics and contributing to the ongoing efforts to advance sustainable energy technologies.

Mixed cations tin-germanium perovskite: A promising approach for enhanced solar cell applications

Significant progress has been made over the years to improve the stability and efficiency of rapidly evolving tin-based perovskite solar cells (PSCs). One powerful approach to enhance the performance of these PSCs is through compositional engineering techniques, specifically by incorporating a mixed cation system at the A-site and B-site structure of the tin perovskite. These approaches will pave the way for unlocking the full potential of tin-based PSCs. Therefore, in this study, a theoretical investigation of mixed A-cations (FA, MA, EA, Cs) with a tin-germanium-based PSC was presented. The crystal structure distortion and optoelectronic properties were estimated. SCAPS 1-D simulations were employed to predict the photovoltaic performance of the optimized tin-germanium material using different electron transport layers (ETLs), hole transport layers (HTLs), active layer thicknesses, and cell temperatures. Our findings reveal that EA0.5Cs0.5Sn0.5Ge0.5I3 has a nearly cubic structure (t = 0.99) and a theoretical bandgap within the maximum Shockley-Queisser limit (1.34 eV). The overall cell performance is also improved by optimizing the perovskite layer thickness to 1200 nm, and it exhibits remarkable stability as the temperature increases. The short-circuit current density (Jsc) remains consistent around 33.7 mA/cm2, and the open-circuit voltage (Voc) is well-maintained above 1 V by utilizing FTO as the conductive layer, ZnO as the ETL, Cu2O as the HTL, and Au as the metal back contact. This configuration also achieves a high fill factor ranging from 87 % to 88 %, with the highest power conversion efficiency (PCE) of 31.49 % at 293 K. This research contributes to the advancement of tin-germanium perovskite materials for a wide range of optoelectronic applications.

Rational design of mixed Sn–Ge based hybrid halide perovskites for optoelectronic applications: a first principles study

Here, we have investigated some mixed metal hybrid halide perovskite materials by employing first principle calculation method. In this regard we have designed some Sn and Ge based hybrid halide (iodide) perovskite materials incorporating dimethylammonium (DMA) organic cation and studied their structural, optoelectronic and photovoltaic properties. Observed tolerance factor (TF) and dihedral factor (μ) manifests that our studied compounds form stable three dimensional perovskite structure. Additionally, the observed negative value of formation energy indicates their thermodynamic stability. Calculated band gap values indicate the semiconducting nature of the compounds. We have also calculated the real and imaginary part of dielectric function as well as absorption coefficient of all the studied compounds. Our investigation reveals that compounds with equal amount of Sn and Ge content exhibit higher value of dielectric function and absorption coefficient among the studied compounds. Study of photovoltaic performances reveal that DMASn_0.75Ge_0.25I₃ exhibits the highest value of theoretical power conversion efficiency (PCE) i.e., 17.42% among the studied compounds. This investigation will help researchers to design Pb-free hybrid perovskite materials which will be beneficial for the world.

Here, we have investigated some mixed metal hybrid halide perovskite materials by employing first principle calculation method.

Tunable ionic conductivity and photoluminescence in quasi-2D CH3NH3PbBr3 thin films incorporating sulphur doped graphene quantum dots

Ion migration in hybrid halide perovskites is ubiquitous in all conditions. However, the ionic conductivity can be manipulated by changing the material composition, operating temperature, light illumination, and applied bias as well as the nature of the interfaces of the devices. There have been various reports on electron ion coupling in hybrid perovskite semiconductors which gives rise to anomalous charge transport behavior in these devices under an applied bias. In this investigation, we have synthesized a mixture of 2D/3D perovskites by incorporating sulphur-doped graphene quantum dots (SGQDs) and demonstrated that the optical and electrical properties of the hybrid system can be tuned by controlling the ion conductivity through the active layer. It has been observed that the recombination resistance in undoped CH₃NH₃PbBr₃ perovskites follows an anomalous behavior while the doped CH₃NH₃PbBr₃ perovskite shows a monotonic increase with increasing applied bias due to reduced ionic conductivity. SGQDs at the grain boundaries of 2D/3D perovskites prohibit ion migration through the active layer, and therefore the electronic-ionic coupling is reduced. This results in increased recombination resistance with increasing applied bias.