"Combining electrical and optical transient measurements to characterize organic solar cells: The impact of light bias"

Autores: Florian Günther, Paulo B. Miranda.

Instituições: Instituto de Física de São Carlos, Universidade de São Paulo.

Autor apresentador: Florian Günther.

Resumo: Research on organic solar cells has increased significantly in the past decade, covering both applied and basic aspects. Improvements in the performances depend on a deep knowledge about the photophysical and electronic processes that occur in the materials. The dynamics of charge recombination within operating devices is one important issue that is relevant for determining the charge recombination losses and the overall device efficiency.

In our work, we directly probe the dynamics of charge recombination and extraction in organic solar cells by combining transient photoinduced absorption spectroscopy (TAS) with transient photovolatge (TPV) or transient photocurrent (TPC) measurements in the ns to ms time range after excitation of the device by a short laser pulse. TAS probes the dynamics of the charge density inside the organic active layer of the solar cell, while TPV determines the electrical potential at the device electrodes and TPC measures rate of charge extraction from the device. Correlating the individual results of those techniques, it is possible to determine fate of photogenerated charge; collection vs. recombination.

Here, we are presenting results obtained from traditional polymer-based (P3HT:PCBM) solar cells. We found that the TAS signal matches the dynamics of extracted charges, independent of a constant illumination (light bias). However, the TAS dynamics becomes shorter and the amount of extracted charge decreases with increasing light bias due to increased recombination loss with the background charges. We furthermore observed that, under open circuit condition and light bias, TPV dynamics measures charge recombination. In contrast, in dark the TAS signals decay much faster than TPV, indicating that free charges are collected at the contacts, which then discharge with the device RC-constant.

Link do vídeo: https://youtu.be/mNHHDM-iSl0

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