PhOG Seminar

Dr. Michael Saliba, École polytechnique fédérale de Lausanne (EPFL), Lausanne, Switzerland
Perovskite Photovoltaics – Opportunities and Challenges towards a Sustainable Energy Future

This presentation gives a general overview of the rapidly evolving field of perovskite solar cells (PSCs). Reasons why perovskite solar cells have triggered such enthusiastic feedback from research groups all over the world are discussed. Additionally, potential drawbacks and challenges are outlined that need to be overcome for industrialising this technology.
The current challenges and approaches of the field are exemplified using a high-performance model systems for PSCs (a triple cesium (Cs), methylammonium (MA), formamidinium (FA) cation perovskite).(1)
The triple cation composition achieves power conversion efficiencies (PCEs) close to 21% and stabilized power outputs at 18% under operational conditions over 250 hours (maximum power point tracking under full illumination held at room temperature). Adding Cs to MA/FA mixtures, which are currently among the highest performing compositions,(2) suppresses yellow phase impurities and induces uniform perovskite grains extending from electron to hole collecting layer consistent with seed-assisted crystal growth. The triple cation perovskites are more robust to subtle variations during the fabrication process enabling a breakthrough in terms of reproducibility where PCEs > 20% were reached on a regular basis (in contrast to the MA/FA only devices).
The principle of mixing cations can be taken further. Through multication engineering, the seemingly too small rubidium (Rb) can be integrated (despite never showing a black phase as a single-cation perovskite).(3)
The composition containing Rb, Cs, MA and FA results in a stabilized efficiency of 21.6% as well as an electroluminescence of 3.8%. The open-circuit voltage of 1.24 V at a band gap of 1.63 eV leads to one of the smallest losses-in-potential (of 0.39 V) ever measured for any PV material. Polymer-coated cells maintained 95% of their initial performance at 85°C for 500 hours under full solar illumination and maximum power point tracking. This is a crucial step towards industrialisation of PSCs.
(1) Saliba et al., Cesium-containing triple cation perovskite solar cells: improved stability, reproducibility and high efficiency. Energy & Environmental Science (2016)
(2) Jeon et al., Compositional engineering of perovskite materials for high-performance solar cells. Nature (2015)
(3) Saliba et al., Incorporation of rubidium cations into perovskite solar cells improves photovoltaic performance. Science (2016)

Wednesday, 09.08.17

15:15 h - 15:45 h

Amalienstr. 54