Precursor Effect on Lead - Tin Mixed Perovskite Solar Cells
Shashini Silva a, Imalka Jayawardena a, Ravi Silva a
a Advanced Technology Institute (ATI), University of Surrey, UK, Guilford, United Kingdom
Proceedings of 13th Conference on Hybrid and Organic Photovoltaics (HOPV21)
Online, Spain, 2021 May 24th - 28th
Organizers: Marina Freitag, Feng Gao and Sam Stranks
Poster, Shashini Silva, 190
Publication date: 11th May 2021

One of the main challenges faced by lead based perovskite solar cells is their inability to achieve narrow bandgap values which limits the highest efficiency a single junction PSC can achieve. This can be overcome by mixing a bit of tin to the B site of the perovskite structure which enables the perovskite absorption layer to achieve narrower bandgaps in the range 1.2 – 1.4 eV. It is in this range that the ideal bandgap at which the maximum conversion efficiency for a solar cell falls as per the Shockley–Queisser limit. However, such Pb-Sn mixed PSCs have not yet achieved their full potential due to the tendency of Sn2+ in the perovskite to get oxidized to Sn4+ thereby leading to deterioration of the photovoltaic performance of the cell.

The photoactive layer thickness is one of the key parameter that needs to be optimized in order to achieve high power conversion efficiencies from a PSC. Thickness of the light absorption layer is directly dependent on the concentration of the perovskite precursor used for spin coating and hence, this study has looked at the effect of precursor concentration on the photovoltaic performance of the solar cell. Our work discovered that the at high concentrations, the devices showed high instability while at the lower end, the short circuit currents achieved by the devices were quite low. Optimal performances were observed at mid-level concentrations with comparably high stabilities along with the better power conversion efficiencies. Analysis of film structures at different precursor concentrations showed that even though the average grain size increased with increase in precursor concentration, a high amount of aggregates were seen at grain boundaries of high concentration films that could act as defect sites which affect adversely on the stability and performance of the PSC.

The authors would like to acknowledge the University of Surrey, Marcus Lee foundation and H2020 CORNET program for funding and support throughout the duration of the project.

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