A Comparative Study of Recombination Mechanisms and Long-Term Outdoor Degradation in Perovskite Solar Cells and Modules Including Self-Assembled Monolayers

Abstract

Perovskite solar cells are one of the most promising photovoltaic technologies in the last decades. Inverted (p–i–n) cells using NiO_X as hole-transport layer (HTL) have gained attention due to their easy fabrication methods and high stability, although they often exhibit reduced efficiencies due to non onlyoptimized energy-level alignment. To address this issue, different approaches have been developed, such as the use of self-assembled monolayers (SAMs) on top of the HTL. Herein, a comparative study between regular p–i–n cells and cells using Me-PACz as an SAM on top of NiO_X is we presented. Devices with SAM exhibit enhanced open-circuit voltage and efficiency. Temperature DC and AC characterization reveals that the incorporation of SAM reduces recombination at the interface, as seen from the comparison of the perovskite bandgap (1.6 eV) and carrier activation energy ≈1.1 and ≈1.59 eV for reference and SAM, respectively. Finally, an outdoor degradation experiment with minimodules has been conducted. The experiment spanned for more than 500 days, and results show that minimodules with SAM were less stable than those based on the reference layer structure. This is due to a severe decrease in the short-circuit current, which could be attributed to a deterioration of the SAM spacer.