Revealing the Role of Spacer Length and Methoxy Substitution of Dipodal Indolocarbazole-based SAMs on the Performance of Inverted Perovskite Solar Cells

Abstract

The application of self-assembled molecules (SAMs) as selective charge transport layers in inverted perovskite solar cells (iPSCs) has attracted significant interest because of their ability to provide high-efficiency and stable devices. In this work, four dipodal SAMs are reported based on π-expanded indolo[2,3-a]carbazole, incorporated as hole-selective contacts in iPSCs. The presence of methoxy substituents and the spacer length in SAMs are modified to assess their influence on the device performance. For that, the ITO/SAM and ITO/SAM/PSCs interfaces are characterized in detail, including theoretical studies and analysis of the complete device performance. These results demonstrate the multifactorial effect that SAMs have on the growth of crystalline perovskite and the charge dynamics in the devices. The resulting iPSCs show power conversion efficiency (PCE) between 19.76% and 22.20% with fill factors exceeding 82% in all cases and good stability under continuous illumination. Notably, SAM combining unsubstituted indolocarbazole and longer pentyl spacer (5CPICZ) shows the highest PCE of 22.20%. In contrast, analogous SAMs with propyl spacers (3CPICZ) achiev a PCE of 22.01%. The experimental results reveal that the improved PCE reached with unsubstituted indolocarbazole SAMs is attributed to reduced charge recombination and longer carrier lifetime owing to effective perovskite surface passivation.