High‐performance tin‐lead perovskite solar cells (PSCs) are needed for all‐perovskite‐tandem solar cells. However, iodide related fast photodegradation severely limits the operational stability of Sn‐Pb perovskites despite the demonstrated high efficiency and thermal stability. Herein, this work employs an alkylammonium pseudo‐halogen additive to enhance the power conversion efficiency (PCE) and photostability of methylammonium (MA)‐free, Sn‐Pb PSCs. Density functional theory (DFT) calculations reveal that the pseudo‐halogen tetrafluoroborate (BF4−) has strong binding capacity with metal ions (Sn2+/Pb2+) in the Sn‐Pb perovskite lattice, which lowers iodine vacancy formation. Upon combining BF4−with an octylammonium (OA+) cation, the PCE of the device with a built‐in light‐scattering layer is boosted to 23.7%, which represents a new record for Sn‐Pb PSCs. The improved efficiency benefits from the suppressed defect density. Under continuous 1 sun illumination, the OABF4embodied PSCs show slower generation of interstitial iodides and iodine, which greatly improves the device photostability under open‐circuit condition. Moreover, the device based on OABF4retains 88% of the initial PCE for 1000 h under the maximum‐power‐point tracking (MPPT) without cooling.
Partial shading of a solar module can induce a set of cells within the module to operate under reverse bias. Studies have shown that metal halide perovskite solar cells with a wide variety of compositions and contacts exhibit interesting behavior in reverse bias that includes both reversible performance loss and non‐reversible degradation. In this paper, an advanced drift‐diffusion approach incorporating an electrochemical term to explain the short‐circuit, open circuit and fill factor losses that are experimentally measured after prolonged reverse bias is used. It is shown that holes can tunnel into the perovskite due to sharp band bending near the contact, accumulate within the bulk of the perovskite absorber, and trigger the oxidation of halides to form neutral halogens. The density of neutral halogens is much higher in reverse bias because there are hardly any electrons available to reduce the iodine. The resulting halogens act as bulk recombination centers. While the interstitial halogen density does decay when the cell is operated in forward bias, permanent degradation can occur if the iodine diffuses out of the perovskite layer. Finally, the ways in which changing parameters such as the mobile ion density or the series resistance at the contact can influence device performance and stability are discussed.
more » « less- NSF-PAR ID:
- 10365567
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Advanced Energy Materials
- Volume:
- 11
- Issue:
- 10
- ISSN:
- 1614-6832
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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