Four-Terminal Tandem Solar Cells Using CH₃NH₃PbBr₃ by Spectrum Splitting

In this work, the use of a high bandgap perovskite solar cell in a spectrum splitting system is demonstrated. A remarkable energy conversion efficiency of 23.4% is achieved when a CH₃NH₃PbBr₃ solar cell is coupled with a 22.7% efficient silicon passivated emitter rear locally diffused solar cell. Relative enhancements of >10% are demonstrated by CH₃NH₃PbBr₃/CH₃NH₃PbI₃ and CH₃NH₃PbBr₃/multicrystalline-screen-printed-Si spectral splitting systems with tandem efficiencies of 13.4% and 18.8%, respectively. The former is the first demonstration of an all perovskite split spectrum system. The CH₃NH₃PbBr₃ cell on a mesoporous structure was fabricated by the vapor-assisted method while the planar CH₃NH₃PbI₃ cell was fabricated by the gas-assisted method. This work demonstrates the advantage of the higher voltage output from the high bandgap CH₃NH₃PbBr₃ cell and its suitability in a tandem system

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

Nucleation and Growth Control of HC(NH₂)₂PbI₃ for Planar Perovskite Solar Cell

HC­(NH₂)₂PbI₃ perovskite solar cells have emerged as a promising alternative to CH₃NH₃PbI₃ perovskite solar cells due to their better thermal stability and lower bandgap. In this work, we have demonstrated a reliable fabrication technique for HC­(NH₂)₂PbI₃ planar perovskite solar cells by controlling nucleation and crystallization processes of the perovskite layer through a combination of gas-assisted spin coating and the addition of HI additive in the perovskite precursor. A narrow distribution of power conversion efficiencies (PCEs) can be achieved with an average of 13% with negligible hysteresis when measured at a scanning rate of 0.1 V/s. The best performance device has a PCE of 16.0%. It is shown that by using optimized conditions we can consistently form dense, uniform, pinhole-free good crystalline, lead-iodide-impurities-free HC­(NH₂)₂PbI₃ film that has been comprehensively characterized by scanning electron microscopy, X-ray diffraction, Kelvin probe force microscopy, photoluminescence, and electroluminescence in this work

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