AEM: Quasi-Fermi level splitting and Voc mismatch in perovskite solar cells

• Perovskite solar cells have low nonradiative voltage losses and an open circuit voltage (VOC) that typically matches the internal voltage in the perovskite layer, known as quasi-Fermi level splitting (QFLS). However, in many cases the VOC differs significantly from the internal voltage, such as in devices without energy alignment. Therefore, understanding this phenomenon is of great significance for further developing perovskite solar cells and solving stability issues.

  
  

  The classical theory developed for silicon solar cells by Jonathan Warby, Dieter Neher, Martin Stolterfoht and others at the University of Potsdam explains the QFLS-VOC mismatch by considering the partial resistance/conductivity of majority and minority carriers.

  
  

  The authors demonstrate that this general theory applies to a variety of physical mechanisms that lead to this mismatch. Furthermore, the study found that in real-life perovskite cells, mobile ions can lead to QFLS-VOC mismatch, which could explain various results regarding light absorption and aging-induced VOC loss.

  The discovery sheds light on a hotly debated topic in the field, identifies a new degradation loss mechanism, and highlights important design principles to maximize VOC in improved perovskite solar cells.

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• Jonathan Warby et.al Mismatch of Quasi–Fermi Level Splitting and Voc in Perovskite Solar Cells Adv. Energy Mater. 2023

  DOI: 10.1002/aenm.202303135

  https://doi.org/10.1002/aenm.202303135