Molecular I2can be produced from iodide‐based lead perovskites under thermal stress; triiodide, I3−, is formed from this I2and I−. Triiodide attacks protic cation MA+‐ or FA+‐based lead halide perovskites (MA+, methylammonium; FA+, formamidinium) as explicated through solution‐based nuclear magnetic resonance (NMR) studies: triiodide has strong hydrogen‐bonding affinity for MA+or FA+, which leads to their deprotonation and perovskite decomposition. Triiodide is a catalyst for this decomposition that can be obviated through perovskite surface treatment with thiol reducing agents. In contrast to methods using thiol incorporation into perovskite precursor solutions, no penetration of the thiol into the bulk perovskite is observed, yet its surface application stabilizes the perovskite against triiodide‐mediated thermal stress. Thiol applied to the interface between FAPbI3and Spiro‐OMeTAD (“Spiro”) prevents oxidized iodine species penetration into Spiro and thus preserves its hole‐transport efficacy. Surface‐applied thiol affects the perovskite work function; it ameliorates hole injection into the Spiro overlayer, thus improving device performance. It helps to increase interfacial adhesion (“wetting”): fewer voids are observed at the Spiro/perovskite interface if thiols are applied. Perovskite solar cells (PSCs) incorporating interfacial thiol treatment maintain over 80% of their initial power conversion efficiency (PCE) after 300 h of 85 °C thermal stress.
Formamidinium (FA)‐based lead iodide perovskites have emerged as the most promising light‐absorber materials in the prevailing perovskite solar cells (PSCs). However, they suffer from the phase‐instability issue in the ambient atmosphere, which is holding back the realization of the full potential of FA‐based PSCs in the context of high efficiency and stability. Herein, the tetraethylorthosilicate hydrolysis process is integrated with the solution crystallization of FA‐based perovskites, forming a new film structure with individual perovskite grains encapsulated by amorphous silica layers that are in situ formed at the nanoscale. The silica not only protects perovskite grains from the degradation but also enhances the charge‐carrier dynamics of perovskite films. The underlying mechanism is discussed using a joint experiment‐theory approach. Through this in situ grain encapsulation method, PSCs show an efficiency close to 20% with an impressive 97% retention after 1000‐h storage under ambient conditions.
more » « less- Award ID(s):
- 1538893
- NSF-PAR ID:
- 10067080
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Advanced Energy Materials
- Volume:
- 8
- Issue:
- 22
- ISSN:
- 1614-6832
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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