Surface passivation of sequentially deposited perovskite solar cells by octylammonium spacer cations

Effective passivation of defects is an important step toward achieving highly efficient and stable Perovskite Solar Cells (PSCs). In this work, we introduce the incorporation of two different octylammonium based spacer cations as 2D perovskite passivation layers, namely Octylammonium Bromide (OABr) and octylammonium iodide. PSCs with OABr as a 2D passivation layer demonstrated an enhanced Power Conversion Efficiency (PCE) of 21.40% (the control device has a PCE of 20.26%), resulting in a higher open circuit voltage of 40 mV. The 2D perovskite passivation layers lead to a smoother interface and a better contact with the hole transport layer, while transient photoluminescence and transient photovoltage measurements indicated reduced non-radiative recombination. Unencapsulated devices retained almost 90% of their initial PCE after 500 h of exposure under high ambient humidity conditions, confirming that the surface passivation treatment has led to improved device stability.