Unraveling the Role of Energy Band Alignment and Mobile Ions on Interfacial Recombination in Perovskite Solar Cells

• Published in: Solar RRL 2022-06, Vol.6 (6), p.n/a
• Main Authors: Mozaffari, Naeimeh, Walter, Daniel, White, Thomas P., Bui, Anh D., Tabi, Grace Dansoa, Weber, Klaus, Catchpole, Kylie R.
• Format: Article
• Language: English
• Subjects: band alignments; charge accumulation; drift diffusion; interfacial recombination; ion movement
• ISSN: 2367-198X; 2367-198X
• DOI: 10.1002/solr.202101087

A key limitation in perovskite solar cell (PSC) performance is suboptimal electronic properties at the perovskite–transport layer (TL) interfaces, which result in parasitic nonradiative recombination. Interface recombination depends on the concentration of recombination‐active defects, but as a recombination event requires both an electron and a hole, the magnitude and sign of charge accumulation at the perovskite–TL heterojunctions are also critical. Here, we employ a well‐established numerical ion‐electron drift‐diffusion model of PSCs to illustrate how the work function of the transport layer is an important factor in determining the total recombination activity at the perovskite interfaces. We show that the equilibrium electrostatics of the perovskite–TL heterojunctions, which are determined by the work function difference between the two materials, can result in increased recombination rates for any given concentration of interface defects. As a case study, we compare PSCs incorporating a NiOX hole transport layer with those with a spiro‐OMeTAD. We show that the work function of NiOX can induce greater electron accumulation at the perovskite–NiOX interface, which leads to increased interface recombination. Finally, a higher ion concentration is found to be beneficial to overall device performance by displacing accumulated electrons or holes at the TL interfaces and thus reducing recombination rates. The energy band alignment at the perovskite–transport layer (TL) heterojunctions determines the interfacial recombination rates. Therefore, some device structures need better passivation to demonstrate high photovoltaic efficiency. Moreover, changes in work function at one TL can affect recombination at the other. Mobile ions can enhance device performance by moving minority carriers away from the interfaces and consequently reduce interface recombination.