Organic–inorganic lead halide perovskite solar cells are regarded as one of the most promising technologies for the next generation of photovoltaics due to their high power conversion efficiency (PCE) and simple solution manufacturing. Among the different compositions, the formamidinium lead iodide (FAPbI3) photoactive phase has a bandgap of 1.4 eV, which enables the corresponding higher PCEs according to the Shockley–Queisser limit. However, the photoactive crystal phase of FAPbI3is not stable at room temperature. The most high‐performing compositions to date have reduced this problem by incorporating the methylammonium (MA) cation into the FAPbI3composition, although MA has poor stability at high temperatures and in humid environments, which can limit the lifetime of FA
Perovskite photovoltaics have made extraordinary progress in power conversion efficiency (PCE) and stability due to process and formulation development. Perovskite cell performance benefits from the addition of alkali metal cations, such as cesium (Cs+) and potassium (K+) in mixed‐ion systems, but the underlying reasons are not fully understood. Herein, the solidification of perovskite layers is studied, incorporating 5%, 10%, to 20% of Cs+and K+using in situ grazing incidence wide‐angle X‐ray scattering. It is found that K+‐doped solutions yield nonperovskite 4H phase rather than the 3C perovskite phase. For Cs+‐doped formulations, both 4H and 3C phases are present at 5% Cs+, whereas the 3C perovskite phase is formed in 10% Cs+‐doped formulations, with undesirable halide segregation occurring at 20% Cs+. Postdeposition thermal annealing converts the intermediate 4H phase to the desirable 3C perovskite phase. Importantly, perovskite layers containing 5% of Cs+or K+exhibit a reduced concentration of trap states and enhanced carrier mobility and lifetime. By carefully adjusting Cs+or K+concentration to 5%, perovskite cells are demonstrated with a ≈5% higher‐average PCE than cells utilizing higher cation concentrations. Herein, unique insights into the crystallization pathways toward perovskite phase engineering and improved cell performance are provided.
- PAR ID:
- 10168801
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Solar RRL
- Volume:
- 4
- Issue:
- 9
- ISSN:
- 2367-198X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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