Mechanistic Origin and Unlocking of Negative Capacitance in Perovskites Solar Cells
| Main Authors: | Khan, Mohd Taukeer, Huang, Peng, Almohammedi, Abdullah, Kazim, Samrana, Ahmad, Shahzada |
|---|---|
| Format: | info publication-preprint Journal |
| Bahasa: | eng |
| Terbitan: |
, 2020
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| Subjects: | |
| Online Access: |
https://zenodo.org/record/4383207 |
Daftar Isi:
- Negative capacitance was found to have an adverse effect on the performance of perovskites solar cells and its origin is still under doubts. Here, we have unlocked the mechanistic behavior of negative capacitance observed at lower and intermediate frequencies by analyzing impedance spectra at variable photovoltage and applied bias, temperature dependent capacitance vs. frequency (C-f) spectra and current-voltage (J-V) characteristics. We noted inverted configuration devices having PEDOT:PSS or PTAA as hole transport layer (HTL) and PCBM as electron transport layer (ETL) exhibit the negative capacitance feature. The activation energies (Ea) for the observance of negative capacitance was found to be (394 meV and 184 meV) in similar order of magnitude required for the ionic migration. Moreover, the kinetic relaxation time (tkin) were also estimated to be 10-1 – 10-2 s and in the same order of magnitude required to activate the halide ion migration in perovskites solar cells. Further, beyond the activation temperature (Ta ~250 K), the trap density (ntrap) increases with no variation in current value signaling the creation of additional traps due to the migration of halide vacancies and recombination of charge carriers in these trap states. Subsequently, charge carrier density reduces and thus negative capacitance was observed. Our investigation suggests that the primary reason for the appearance of negative capacitance in perovskites solar cells with p-i-n (inverted planar) configuration is associated with the migration of halide vacancies in the perovskites layer.