Solar technology: degradation modes and de-risking practical development
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The commercialisation of a solar technology necessitates the fulfilment of specific requirements both regarding efficiency and stability to enter and gain space in the photovoltaic market. These aims are heavily dependent on the selection of suitable materials, which is crucial for suppressing any reliability risks arising from inherent instabilities.
In this paper*, published by Advanced Energy Materials and co-authored by Professor M Saiful Islam and collaborators from Oxford Photovoltaics Limited and the Departments of Physics at the University of Oxford and University of Lancaster, the most suitable low bandgap lead-tin composition candidate for all-perovskite tandem applications was investigated as an absorber material by studying the degradation mechanisms with both widely available and advanced characterisation techniques.
Three irreversible degradation processes were identified in narrow bandgap Pb-Sn perovskite absorbers:
1) Tin (Sn) oxidation upon air exposure;
2) Methylammonium (MA) loss upon heat exposure; and
3) Formamidinium (FA) and cesium (Cs) segregation leading to impurity phase formation.
From an industrial perspective, the authors propose to refocus attention on FASn0.5Pb0.5I3 which minimises all three effects while maintaining a suitable bandgap for a bottom cell and good performance. Moreover, a practical and highly sensitive characterisation method is proposed to monitor the oxidation, which can be deployed both in laboratory and industrial environments and provide useful information for the technological development process, including the effectiveness of encapsulation methods and the acceptable time windows for air exposure.
