Stability and Performance of CsPbI₂Br Thin Films and Solar Cell Devices

Abstract

In this manuscript, the inorganic perovskite CsPbIBr is investigated as a photovoltaic material that offers higher stability than the organic-inorganic hybrid perovskite materials. It is demonstrated that CsPbIBr does not irreversibly degrade to its component salts as in the case of methylammonium lead iodide but instead is induced (by water vapor) to transform from its metastable brown cubic (1.92 eV band gap) phase to a yellow phase having a higher band gap (2.85 eV). This is easily reversed by heating to 350 °C in a dry environment. Similarly, exposure of unencapsulated photovoltaic devices to water vapor causes current (J) loss as the absorber transforms to its more transparent (yellow) form, but this is also reversible by moderate heating, with over 100% recovery of the original device performance. NMR and thermal analysis show that the high band gap yellow phase does not contain detectable levels of water, implying that water induces the transformation but is not incorporated as a major component. Performances of devices with best efficiencies of 9.08% (V = 1.05 V, J = 12.7 mA cm and FF = 68.4%) using a device structure comprising glass/ITO/c-TiO/CsPbIBr/Spiro-OMeTAD/Au are presented, and further results demonstrating the dependence of the performance on the preparation temperature of the solution processed CsPbIBr films are shown. We conclude that encapsulation of CsPbIBr to exclude water vapor should be sufficient to stabilize the cubic brown phase, making the material of interest for use in practical PV devices.

Synergy of Hydrophobic Surface Capping and Lattice Contraction for Stable and High‐Efficiency Inorganic CsPbI2Br Perovskite Solar Cells

“…Later, the dual halide CsPbI 2 Br was developed, and it has great advantages in terms of ambient phase stability and a more suitable band gap (1.91 eV) . Further study confirmed that the desired black phase CsPbI 2 Br is indeed tolerant to a range of degradation factors; however, it turns into the non‐perovskite orthorhombic phase upon exposure to a humid environment or water vapor . Hence, it is imperative to protect it against moisture ingress.…”

“…[23][24][25] Further study confirmed that the desired black phase CsPbI 2 Br is indeed tolerant to a range of degradation factors [26,27] ; however, it turns into the non-perovskite orthorhombic phase upon exposure to a humid environment or water vapor. [28,29] Hence, it is imperative to protect it against moisture ingress.…”

Stability Issue of Perovskite Solar Cells under Real‐World Operating Conditions

“…Thermal stability is a very important criterion for the commercialization of OIHP‐based solar cells. The OIHP usually undergoes degradation or phase transformation under long‐term high‐temperature stress . The thermal instability of PSCs can be mainly ascribed to the low thermal conductivity of the OIHP layer.…”

Anorganische CsPbX3‐Perowskit‐Solarzellen: Fortschritte und Perspektiven

“…So wurden optimale Zellen erhalten, wenn CsPbBr 3 bei 250 8 8Ca nd er Luft getempert wurde. [61] Sie fanden, dass von den Parametern Feuchtigkeit, Sauerstoff,U V-Licht (365 nm), Innenlicht und UV + O 3 Wasserdampf der einzige Parameter war, der das HaP deutlich abbaute. 550 8 8Ct hermisch stabil ist und dass die Zersetzung zudem auf den Verlust von PbBr 2 und nicht von CsBr zurückzuführen ist.…”