Original Article:
Rubidium Iodide Reduces Recombination Losses in Methylammonium-Free Tin-Lead Perovskite Solar Cells
Fengjiu Yang, et al.
Advanced Energy Materials, 2023, 2204339.
10.1002/aenm.202204339
Metal halide perovskite materials have attracted extensive attention due to their promising applications as solar cell absorbers. Alkali metal salts such as rubidium iodide (RbI) and potassium iodide (KI) are used as dopants in Sn-Pb perovskites containing methylammonium (MA) to improve crystallinity and carrier lifetime, and reduce Composite resistance. However, the working mechanisms of these alkali metal salts, such as their physical distribution within thin films, their interactions with Sn vacancies, and their effects on interfacial and bulk recombination are not well understood. One of the goals of this work is to gain a better understanding of these processes to further improve the performance of perovskite solar cells (PSCs) through rational design of processing schemes.
Effects of RbI Additive in PSCs
- RbI additives lead to a redistribution of elements within the film, resulting in a new composition of FA0.83Cs0.17Sn0.5Pb0.5I3. The composition exhibits a change in lattice strain, as well as a compositional gradient from the film surface to the bulk.
- Quasi-Fermi level splitting (QFLS) and transient photoluminescence (trPL) measurements show that the RbI-containing perovskite samples exhibit improved performance after storage for one week, reaching a peak QFLS of 0.925 eV.
- The nonradiative recombination losses at the perovskite/C60 and perovskite/PEDOT:PSS interfaces are lower in the RbI-containing perovskite samples.
- The carrier lifetime of the RbI-containing perovskite on the quartz substrate is significantly longer, increasing from the reference value of 1.46 µs to 9.46 µs.
- The PCE of RbI-containing Sn-Pb PSCs exceeds 20%, and the VOC is 0.823 V (18.32% PCE and 0.762 V VOC for the reference device).
Mechanism of RbI Additive in PSCs
- High-sensitivity photoelectron yield spectroscopic measurements at constant final state (CFSYS) reveal a tenfold reduction in the surface defect density of RbI-containing perovskites.
- Hall-effect measurements show that the hole carrier concentration in the RbI-containing sample is reduced by nearly two orders of magnitude and the resistivity is increased.
- RbI incorporation leads to an increase in the Fermi level, making the perovskite more intrinsic.
- RbI reduces hysteresis and current loss caused by moving ions.
Preparation of RbI-modified Sn-Pb PSCs
1. The FA0.83Cs0.17Sn0.5Pb0.5I3 perovskite precursor was prepared by mixing FAI, CsI, PbI2, SnI2, SnF2, and Pb(SCN)2 in the DMF/DMSO solution and dissolved in a shaker at room temperature.
2. As for the RbI additive samples, the concentration of RbI was dissolved in DMF/DMSO (4:1 in V:V) with the same as the perovskite precursor.
3. The dissolved RbI solution was filtered by using a PTFE filter before mixing with the perovskite precursor in different volume ratios. The RbI-containing perovskite precursor was used with the spin coating and annealing procedures after shaking.
4. Afterwards, 23 nm of C60 and 8 nm of BCP were continuously thermally evaporated on the perovskite surface.
5. Finally, the 100 nm of Cu was thermally deposited to define 6 cells per glass substrate.
Chemicals Related in the Paper:
| Catalog Number | Product Name | Structure | CAS Number | Price |
|---|---|---|---|---|
| ACM7790296 | Rubidium iodide |  |
7790-29-6 | Price |
