Surface-Activated Corrosion in Tin–Lead Halide Perovskite Solar Cells

Abstract

Mixed tin–lead halide perovskite solar cells have promising power conversion efficiencies, but long-term stability is still a challenge. Herein we examine the stability of a 60:40 tin–lead perovskite to better understand diminished device performance upon thermal treatment, both in ambient and inert atmosphere. Operando X-ray diffraction shows a stable bulk structure of the perovskite absorber, leading to the hypothesis that surface chemistry dominates the degradation mechanism. X-ray photoelectron spectroscopy reveals two new observations post-thermal annealing that accompany previously reported Sn4+ evolution: (i) the formation of I3 – intermediates preceding I2 loss at the surface and (ii) evidence of under-coordinated tin and lead surface sites (Snδ<2+ and Pbδ<2+, respectively) in inert and ambient conditions. These two species indicate an activated corrosion (i.e., both oxidation and reduction) process at the surface as a possible chemical pathway for degradation, which is expected to be accelerated under operando voltage and light biases.

High-performance hysteresis-free perovskite transistors through anion engineering

“…Furthermore, previous studies have suggested that the incorporation of anions with electronegativity stronger than that of I − raises the V Sn formation energy during perovskite crystallisation, further reducing the hole concentration 24,42 . Additionally, for both the I-pristine and I/Br samples, a small shoulder peak appeared at a low binding energy (~485.4 eV), which is ascribed to under-coordinated Sn with an oxidation state of δ < 2 + (Sn δ< 2+ ) 43 . However, this shoulder peak was undetectable in both the I/Cl and I/Br/Cl samples, indicating well-coordinated Sn sublattices and reduced structural imperfections.…”

Proton‐Radiation Tolerant All‐Perovskite Multijunction Solar Cells

“…In contrast to perovskite single junction [ 13,14,16,17,24 ] and perovskite/CIGS [ 18 ] tandem solar cells that use well‐studied compositionally stable radiation‐hard perovskite absorber compositions [ 10,12,15–17 ] with a bandgap of ≈1.6 eV, the high‐gap and low‐gap perovskite compositions required for all‐perovskite tandem PV thus face additional potential degradation issues under harsh radiation conditions. The phase‐separation of mixed perovskites with high bandgap as well as the oxidation of Sn 2+ to Sn 4+ in low‐gap perovskites is known to be triggered by intense and/or prolonged illumination, [ 22,25 ] heat [ 26 ] or γ‐irradiation. [ 27 ] Harsh particle irradiation excites both, the nuclear and electronic subsystems, [ 28 ] and thus heat as well as charge‐induced degradation mechanisms are likely triggered.…”

“…Moreover, recent reports on thermal degradation of PEDOT:PSS/low‐gap perovskite systems have shown that PEDOT:PSS can cause the oxidation of Sn of the low‐gap Pb‐Sn alloyed perovskite, likely activated from the surface. [ 26,81 ] Therefore, in the specific architecture and as shown in Figure 6, the damaged recombination layer may lead to a barrier to charge quenching from the high‐gap perovskite to the C 60, thus increasing the PL intensity of that absorber relative to the pristine control, while the damaged, more‐conductive PEDOT will better quench the PL from the low‐gap cell (cf. Figure 4a).…”

A Perspective on the Commercial Viability of Perovskite Solar Cells

“…[ 79,80 ] Substitution of lead (Pb) by tin (Sn) in the B‐site of the perovskite lattice further narrowed the energy gap from 1.31 to 1.1 eV (Figure 2d), with a PCE of ≈12% for Pb:Sn = 1:1. [ 81–85 ] Even though pure tin‐based halide has a narrower energy gap compared with its lead‐based counterpart, with the highest PCE recorded at 12.4%, the stability needs to be further improved for commercialization. [ 86–88 ]…”

“…[79,80] Substitution of lead (Pb) by tin (Sn) in the B-site of the perovskite lattice further narrowed the energy gap from 1.31 to 1.1 eV (Figure 2d), with a PCE of %12% for Pb:Sn ¼ 1:1. [81][82][83][84][85] Even though pure tin-based halide has a narrower energy gap compared with its lead-based counterpart, with the highest PCE recorded at 12.4%, the stability needs to be further improved for commercialization. [86][87][88] Other than flexibility in energy gap tuning, ambipolar transport properties of halide perovskite materials have also attracted considerable attention for applications other than PVs.…”