| AVS 62nd International Symposium & Exhibition | |
| Scanning Probe Microscopy Focus Topic | Wednesday Sessions |
| Session SP+AS+NS+SS-WeM |
| Session: | Advances in Scanning Probe Microscopy |
| Presenter: | Nicolas Chevalier, Univ. Grenoble Alpes/ CEA, LETI, MINATEC Campus, France |
| Authors: | N. Chevalier, Univ. Grenoble Alpes/ CEA, LETI, MINATEC Campus, France S. Pouch, Univ. Grenoble Alpes/ CEA, LETI, MINATEC Campus, France D. Mariolle, Univ. Grenoble Alpes/ CEA, LETI, MINATEC Campus, France B. Grevin, Univ. Grenoble Alpes/ CEA, INAC, SPrAM, LEMOH, France Ł. Borowik, Univ. Grenoble Alpes/ CEA, LETI, MINATEC Campus, France |
| Correspondent: | Click to Email |
The photo-carrier lifetime plays a major role in the overall efficiency of a solar cell because it limits the proportion of photo-generated charges collected at the electrodes. This lifetime, which should be ideally as large as possible in an organic or inorganic solar cell, is rather difficult to measure in nanostructured materials or in more complex hybrid systems, indirect band-gap semiconductors, and ultra-thin layers. Identifying the losses mechanisms is one of the main objectives for increasing the performances of solar cells. Most of the experimental approaches developed so far consist in studying recombination by techniques such as transient photovoltage measurements or charge extraction. All these techniques average sample properties over macroscopic scales, making them unsuitable for directly assessing the impact of local heterogeneity on the recombination process. In this paper, we propose a steady method to measure the photo carrier lifetime by photo-modulated techniques based on Kelvin probe force microscopy (KPFM). [1] Additionally, KPFM technique provides a spatially resolved measurement, which is applicable on the overall of solar cells.
We will present the principle of this original method based on the measurement of the surface potential by KPFM under an illumination with a rectangular waveform light modulation. Photo-carrier lifetime down to µs scale is reachable with our experimental setup. The modulation-dependent surface potential is plotted as a function of the frequency. Assuming an immediate generation time under illumination and an exponential decay of the surface potential during the dark condition, the averaged surface potential over a cycle can be fitted as a function of the frequency by simple equation where the only fit parameter is the photocarrier-lifetime. [2] Instrumental aspects as well as data treatment will be reviewed. Measurements obtained on silicon nanocrystals embedded in 30 nm film of silicon dioxide [3] and on organic donor-acceptor blend (PBTFB and PCBM) [4] will be presented to illustrate the potential of the technique.
This work was supported by the French “Recherche Technologique de Base” Program and performed in the frame of the trSPV Nanoscience project. The measurements were performed on the CEA Minatec Nanocharacterization Platform (PFNC).
1. Ł. Borowik et al. Phys. Rev. B 82, 073302 (2010).
2. Ł. Borowik et al. Nanotechnology 25, 265703 (2014).
3. D. Asakura et al. Phys. Rev. Lett. 93, 247006 (2004).
4. N. Delbosc et al. RSC Adv 4, 15236 (2014).