Optical absorptance spectroscopy of polycrystalline CHNHPbI films usually indicates the presence of a PbI phase, either as a preparation residue or due to film degradation, but gives no insight on how this may affect electrical properties. Here, we apply photocurrent spectroscopy to both perovskite solar cells and coplanar-contacted layers at various stages of degradation. In both cases, we find that the presence of a PbI phase restricts charge-carrier transport, suggesting that PbI encapsulates CHNHPbI grains. We also find that PbI injects holes into the CHNHPbI grains, increasing the apparent photosensitivity of PbI. This phenomenon, known as modulation doping, is absent in the photocurrent spectra of solar cells, where holes and electrons have to be collected in pairs. This interpretation provides insights into the photogeneration and carrier transport in dual-phase perovskites.
|Original language||English (US)|
|Number of pages||6|
|Journal||The Journal of Physical Chemistry Letters|
|State||Published - Feb 6 2017|
Bibliographical noteKAUST Repository Item: Exported on 2020-10-01
Acknowledgements: The authors acknowledge financial support from Czech Science Foundation Project No. 17-26041Y, the Project KONNECT- 007 of the Czech Academy of Sciences, the Czech Ministry of Education, Youth and Sports Projects LM2015087 and CZ.02.1.01/0.0/0.0/15_003/0000464 Centre of Advanced Photovoltaics, and the Swiss National Science Foundation through Nanotera and PNR 70 program. We thank Prof. Roman Grill and Dr. Thomas Dittrich for fruitful discussions.