Abstract
Tetragonal phases for perovskite solar cells
The power conversion efficiencies (PCEs) of all-inorganic perovskites are lower than those of materials with organic cations. This is in part because these materials have larger bandgaps. The cubic crystal phases of these materials also exhibit poor stability. Wang
et al.
synthesized the tetragonal β-phase of CsPbI
3
from HPbI
3
and CsI. The material exhibited higher stability and a more favorable bandgap, which allowed for PCEs of 15%. Passivation of the surface trap state with choline iodide boosted PCEs to 18%.
Science
, this issue p.
591
The more stable orthorhombic phase of CsPbI
3
yields more efficient solar cells.
Although β-CsPbI
3
has a bandgap favorable for application in tandem solar cells, depositing and stabilizing β-CsPbI
3
experimentally has remained a challenge. We obtained highly crystalline β-CsPbI
3
films with an extended spectral response and enhanced phase stability. Synchrotron-based x-ray scattering revealed the presence of highly oriented β-CsPbI
3
grains, and sensitive elemental analyses—including inductively coupled plasma mass spectrometry and time-of-flight secondary ion mass spectrometry—confirmed their all-inorganic composition. We further mitigated the effects of cracks and pinholes in the perovskite layer by surface treating with choline iodide, which increased the charge-carrier lifetime and improved the energy-level alignment between the β-CsPbI
3
absorber layer and carrier-selective contacts. The perovskite solar cells made from the treated material have highly reproducible and stable efficiencies reaching 18.4% under 45 ± 5°C ambient conditions.