Max-Planck-Institute for Solid State Research, Heisenbergstraße 1, 70569 Stuttgart (Germany).
Department of Chemistry and Chemical Engineering, Swiss Federal Institute of Technology, Station 6, 1015 Lausanne (Switzerland).
Angew Chem Int Ed Engl. 2015 Jun 26;54(27):7905-10. doi: 10.1002/anie.201500014. Epub 2015 May 15.
The success of perovskite solar cells has sparked enormous excitement in the photovoltaic community not only because of unexpectedly high efficiencies but also because of the future potential ascribed to such crystalline absorber materials. Far from being exhaustively studied in terms of solid-state properties, these materials surprised by anomalies such as a huge apparent low-frequency dielectric constant and pronounced hysteretic current-voltage behavior. Here we show that methylammonium (but also formamidinium) iodoplumbates are mixed conductors with a large fraction of ion conduction because of iodine ions. In particular, we measure and model the stoichiometric polarization caused by the mixed conduction and demonstrate that the above anomalies can be explained by the build-up of stoichiometric gradients as a consequence of ion blocking interfaces. These findings provide insight into electrical charge transport in the hybrid organic-inorganic lead halide solar cells as well as into new possibilities of improving the photovoltaic performance by controlling the ionic disorder.
钙钛矿太阳能电池的成功在光伏界引起了极大的兴奋，不仅因为其出人意料的高效率，还因为这种晶状吸收材料具有未来潜力。这些材料在固态性能方面远未得到详尽研究，它们通过异常现象令人惊讶，例如巨大的表观低频介电常数和明显的滞后电流-电压行为。在这里，我们表明，碘化甲基铵（以及碘化甲脒）钙钛矿是具有大量离子传导的混合导体，这是由于碘离子的存在。特别是，我们测量并建模了由混合传导引起的化学计量极化，并证明上述异常现象可以通过离子阻塞界面引起的化学计量梯度的建立来解释。这些发现为理解混合有机-无机卤化铅太阳能电池中的电荷输运提供了深入的见解，并为通过控制离子无序来提高光伏性能提供了新的可能性。
