Vladimir Dyakonov: Transient electrical studies probing charge carrier recombination in organic and hybrid solar cells

Hybrid perovskite solar cells are progressing very fast, showing extraordinary performance competing with inorganic thin-film technologies. We performed open circuit voltage decay (OCVD) measurements on methylammonium lead iodide (CH₃NH₃PbI₃) perovskite solar cells to increase the understanding of the charge carrier recombination dynamics in this emerging technology. Optically pulsed OCVD measurements are conducted on CH₃NH₃PbI₃ solar cells and compared to results from another type of thin-film photovoltaics, namely, the two reference polymer–fullerene bulk heterojunction solar cell devices based on P3HT:PC₆₀BM and PTB7:PC₇₀BM blends. [1] We observe two very different time domains of the voltage transient in the perovskite solar cell with a first drop on a short time scale that is similar to the decay in the studied organic solar cells. However, 65%–70% of the maximum photovoltage persists on much longer timescales in the perovskite solar cell than in the organic devices. In addition, we find that the recombination dynamics in all time regimes are dependent on the starting illumination intensity, which is also not observed in the organic devices.

In the second part of the talk, I will address the role of spin on the performance of organic solar cells under real operation conditions. Here, we combined electrically detected magnetic resonance (EDMR) with the quantitative technique open circuit corrected transient charge extraction (OTRACE). Extracting photo-generated charges under magnetic resonant conditions compared to non-resonant conditions yields a surprisingly low influence of spins on the non-geminate recombination process.

[1]         A. Baumann et al., Appl. Phys. Lett. Mater. 2014, 2, 081501.