CsPbIBr₂ Perovskite Solar Cell by Spray-Assisted Deposition

In this work, an inorganic halide perovskite solar cell using a spray-assisted solution-processed CsPbIBr₂ film is demonstrated. The process allows sequential solution processing of the CsPbIBr₂ film, overcoming the solubility problem of the bromide ion in the precursor solution that would otherwise occur in a single-step solution process. The spraying of CsI in air is demonstrated to be successful, and the annealing of the CsPbIBr₂ film in air is also successful in producing a CsPbIBr₂ film with an optical band gap of 2.05 eV and is thermally stable at 300 °C. The effects of the substrate temperature during spraying and the annealing temperature on film quality and device performance are studied. The substrate temperature during spraying is found to be the most critical parameter. The best-performing device fabricated using these conditions achieves a stabilized conversion efficiency of 6.3% with negligible hysteresis. Cesium metal halide perovskites remain viable alternatives to organic metal halide perovskites as the cesium-containing perovskites can withstand higher temperature

Strontium-Doped Low-Temperature-Processed CsPbI₂Br Perovskite Solar Cells

Cesium (Cs) metal halide perovskites for photovoltaics have gained research interest due to their better thermal stability compared to their organic–inorganic counterparts. However, demonstration of highly efficient Cs-based perovskite solar cells requires high annealing temperature, which limits their use in multijunction devices. In this work, low-temperature-processed cesium lead (Pb) halide perovskite solar cells are demonstrated. We have also successfully incorporated the less toxic strontium (Sr) at a low concentration that partially substitutes Pb in CsPb_1–<i>x</i>Sr_<i>x</i>I₂Br. The crystallinity, morphology, absorption, photoluminescence, and elemental composition of this low-temperature-processed CsPb_1–<i>x</i>Sr_<i>x</i>I₂Br are studied. It is found that the surface of the perovskite film is enriched with Sr, providing a passivating effect. At the optimal concentration (<i>x</i> = 0.02), a mesoscopic perovskite solar cell using CsPb_0.98Sr_0.02I₂Br achieves a stabilized efficiency at 10.8%. This work shows the potential of inorganic perovskite, stimulating further development of this material

Water-Free, Conductive Hole Transport Layer for Reproducible Perovskite–Perovskite Tandems with Record Fill Factor

State-of-the-art perovskite–perovskite tandem solar cells incorporate a water-based poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) hole transport layer in its low bandgap subcell. However, there is a limitation regarding its use due to the moisture sensitivity of perovskites and the insulating property of PSS. Here, we overcome the limitation by using a water-free and PSS-free PEDOT-based hole transport layer for low bandgap single-junction perovskite solar cells and in perovskite–perovskite tandems. The champion tandem cell produces an efficiency of 21.5% and a fill factor of 85.8%, the highest for any perovskite-based double-junction tandems. Results of photoelectron spectroscopy, Fourier-transform infrared spectroscopy, and conductive atomic force microscopy reveal evidence of enhanced conductivity of water-free and PSS-free PEDOT compared to its conventional counterpart. The use of water-free and PSS-free PEDOT also eliminates decomposition of high bandgap subcell with its interfacing layer stack in a tandem that otherwise occurs with conventional PEDOT:PSS. This leads to enhanced reproducibility of perovskite–perovskite tandems

High-Efficiency Rubidium-Incorporated Perovskite Solar Cells by Gas Quenching

We apply gas quenching to fabricate rubidium (Rb) incorporated perovskite films for high-efficiency perovskite solar cells achieving 20% power conversion efficiency on a 65 mm² device. Both double-cation and triple-cation perovskites containing a combination of methylammonium, formamidinium, cesium, and Rb have been investigated. It is found that Rb is not fully embedded in the perovskite lattice. However, a small incorporation of Rb leads to an improvement in the photovoltaic performance of the corresponding devices for both double-cation and triple-cation perovskite systems

The Effect of Stoichiometry on the Stability of Inorganic Cesium Lead Mixed-Halide Perovskites Solar Cells

Metal halide perovskite solar cells that use the inorganic cation Cs have been shown to have better thermal stability than the organic cation containing counterparts, and CsPbI₂Br has a more suitable (lower) band gap than CsPbIBr₂ as a photovoltaic energy harvesting material. However, increase in iodine content reduces structural stability due to the preference toward the non-perovskite orthorhombic phase when the film is exposed to air. In this work, the effect of varying stoichiometry of CsPbI₂Br perovskite on film quality such as the grain size, presence of impurities and nature of impurity grains, photoluminescence, morphology, and elemental distribution are studied. Details on how to vary the stoichiometry during the dual source thermal evaporation process are reported. It is found that the air stability of CsPbI₂Br film correlates with the CsBr-to-PbI₂ deposition rate ratio, in which the CsBr-rich CsPbI₂Br is the most stable upon air exposure, while the stoichiometrically balanced CsPbI₂Br perovskite film gives the best photovoltaic performance. The encapsulated device maintains 90% of the initial performance after 240 h damp and heat test at 85 °C and 85% relative humidity

Overcoming the Challenges of Large-Area High-Efficiency Perovskite Solar Cells

For the first time, we report large-area (16 cm²) independently certified efficient single perovskite solar cells (PSCs) by overcoming two challenges associated with large-area perovskite solar cells. The first challenge of realizing a homogeneous and densely packed perovskite film over a large area is overcome by using an antisolvent spraying process. The second challenge of removing the series resistance limitation of transparent conductor is overcome by incorporating a metal grid designed using a semidistributed diode model. A 16 cm² perovskite solar device at the cell level rather than at the module level is demonstrated using the modified solution process in conjunction with the use of a metal grid. The cell is independently certified to be 12.1% efficient. This work paves the way toward highly efficient and large perovskite cells without single-junction perovskite solar cells and silicon–perovskite tandems

Overcoming the Challenges of Large-Area High-Efficiency Perovskite Solar Cells

For the first time, we report large-area (16 cm²) independently certified efficient single perovskite solar cells (PSCs) by overcoming two challenges associated with large-area perovskite solar cells. The first challenge of realizing a homogeneous and densely packed perovskite film over a large area is overcome by using an antisolvent spraying process. The second challenge of removing the series resistance limitation of transparent conductor is overcome by incorporating a metal grid designed using a semidistributed diode model. A 16 cm² perovskite solar device at the cell level rather than at the module level is demonstrated using the modified solution process in conjunction with the use of a metal grid. The cell is independently certified to be 12.1% efficient. This work paves the way toward highly efficient and large perovskite cells without single-junction perovskite solar cells and silicon–perovskite tandems