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Capacitance-based techniques have been used to measure the electrical properties of halide perovskite solar cells (PSCs) such as defect activation energy and density, carrier concentration, and dielectric constant, which provide key information for evaluating the device performance. Here, we show that capacitance-based techniques cannot be used to reliably analyze the properties of defects in the perovskite layer or at its interface, since the high-frequency capacitance signature is due to the response of charge carriers in the hole-transport layer (HTL). For HTL-free PSCs, the high-frequency capacitance can be considered as the geometric capacitance for analyzing the dielectric constant of the perovskite layer, since there is no trapping and de-trapping of charge carriers in the perovskite layer. We further find that the low-frequency capacitance signature can be used to calculate the activation energy of the ionic conductivity of the perovskite layer, but the overlapping effects with charge transport materials must be avoided.
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In praise and in search of highly-polarizable semiconductors: Technological promise and discovery strategies
The dielectric response of materials underpins electronics and photonics. At high frequencies, dielectric polarizability sets the scale for optical density and absorption. At low frequencies, dielectric polarizability determines the band diagram of junctions and devices, and nonlinear effects enable tunable capacitors and electro-optic modulators. More complicated but no less important is the role of dielectric response in screening bound and mobile charges. These effects control defect charge capture and recombination rates, set the scale for insulator-metal transitions, and mediate interactions among charge carriers and between charge carriers and phonons. In this perspective, we motivate the discovery of highly polarizable semiconductors by highlighting their potential to improve existing and enable new optoelectronic device technologies. We then suggest discovery strategies based on solid state chemical principles and building on recent efforts in computational materials screening.
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- Award ID(s):
- 1751736
- PAR ID:
- 10594713
- Publisher / Repository:
- American Institute of Physics
- Date Published:
- Journal Name:
- APL Materials
- Volume:
- 7
- Issue:
- 10
- ISSN:
- 2166-532X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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