Advanced spectroscopy of organic and hybrid photovoltaic materials and thin-film solar cells
Event details
| Date | 18.05.2017 |
| Hour | 16:00 › 17:00 |
| Speaker |
Prof. Vladimir Dyakonov Experimental Physics, Faculty of Physics and Astronomy, Julius-Maximillian University of Würzburg and Bavarian Center for Applied Energy Research, Würzburg, Germany |
| Location | |
| Category | Conferences - Seminars |
ChE-602 - Recent Events in Energy seminar series
Organic and recently particularly hybrid (perovskite) thin-film solar cells are progressing very fast, showing extraordinary performance. However, there is still a lack of fundamental understanding of charge carrier transport and recombination losses in these types of solar cells. The charge carrier lifetime and the mobility are two very important parameters in solar cells, as they define the diffusion length of the charge carriers and thus the efficiency. To determine them, various optical and electrical techniques can be applied. We will discuss the peculiarities and limitations of transient photo-voltage and photo-current techniques, such as open circuit voltage decay (OCVD), the small-perturbation transient photo-voltage (TPV) and charge extraction (CE) and the time-of flight (TOF). To fully understand recombination mechanisms in solar cells, it is essential to evaluate them under as large a range of illumination intensities as possible to assess which recombination pathway becomes dominant under each corresponding carrier concentration. As an example, we will discuss the OCVD technique. There we observed several time domains in the voltage transient. On a short timescale, a voltage drop due to free charge carrier recombination is observed and transients are qualitatively similar in organic and perovskite solar cells. [1] On longer times, a rapid voltage drop is often observed, however, these losses are not associated with the absorber material itself, but rather with the entire device. They are due to so-called shunts, which act as additional recombination pathway. By the proper choice of transport materials, it is however possible to remove the shunts and to study the devices under reduced illumination conditions, as charge carriers are efficiently blocked from recombining at the electrodes. [2]
Finally, to address the possible influence of electronic trap states on device performance, we probed the traps in organic and perovskite solar cells via thermally stimulated current (TSC) analysis. In this method the sample is initially cooled down, where trap states are subsequently filled optically. Then, the current flow is monitored upon heating the device up again. This very small current is attributed to charge carriers being thermally released from trap sites in the semiconductor bulk or at the interfaces, which allows to draw conclusions about their energy distribution, depth and density. [3] We will also discuss the influence of the chemical composition as well as morphology on the energetic trap landscape.
[1] A. Baumann et al., Appl. Phys. Lett. Mater. 2, 081501 (2014).
[2] K. Tvingstedt et al., ACS Energy Lett. 2, 424 (2017).
[3] A. Baumann et al., J. Phys. Chem. Lett. 6, 2350 (2015).
Organic and recently particularly hybrid (perovskite) thin-film solar cells are progressing very fast, showing extraordinary performance. However, there is still a lack of fundamental understanding of charge carrier transport and recombination losses in these types of solar cells. The charge carrier lifetime and the mobility are two very important parameters in solar cells, as they define the diffusion length of the charge carriers and thus the efficiency. To determine them, various optical and electrical techniques can be applied. We will discuss the peculiarities and limitations of transient photo-voltage and photo-current techniques, such as open circuit voltage decay (OCVD), the small-perturbation transient photo-voltage (TPV) and charge extraction (CE) and the time-of flight (TOF). To fully understand recombination mechanisms in solar cells, it is essential to evaluate them under as large a range of illumination intensities as possible to assess which recombination pathway becomes dominant under each corresponding carrier concentration. As an example, we will discuss the OCVD technique. There we observed several time domains in the voltage transient. On a short timescale, a voltage drop due to free charge carrier recombination is observed and transients are qualitatively similar in organic and perovskite solar cells. [1] On longer times, a rapid voltage drop is often observed, however, these losses are not associated with the absorber material itself, but rather with the entire device. They are due to so-called shunts, which act as additional recombination pathway. By the proper choice of transport materials, it is however possible to remove the shunts and to study the devices under reduced illumination conditions, as charge carriers are efficiently blocked from recombining at the electrodes. [2]
Finally, to address the possible influence of electronic trap states on device performance, we probed the traps in organic and perovskite solar cells via thermally stimulated current (TSC) analysis. In this method the sample is initially cooled down, where trap states are subsequently filled optically. Then, the current flow is monitored upon heating the device up again. This very small current is attributed to charge carriers being thermally released from trap sites in the semiconductor bulk or at the interfaces, which allows to draw conclusions about their energy distribution, depth and density. [3] We will also discuss the influence of the chemical composition as well as morphology on the energetic trap landscape.
[1] A. Baumann et al., Appl. Phys. Lett. Mater. 2, 081501 (2014).
[2] K. Tvingstedt et al., ACS Energy Lett. 2, 424 (2017).
[3] A. Baumann et al., J. Phys. Chem. Lett. 6, 2350 (2015).
Practical information
- General public
- Free