Dual Strategies with Defect Suppression and Hole Transporting Bilayer for Inverted Perovskite Solar Cell (PCE ~24%)

A growing interest in inverted structure perovskite solar cells (i-PSCs) is underway due to their higher stability and potential applications in tandem structures. Typical organic/polymeric hole-transporting layers (HTLs) often faced limitations in improving stability due to intrinsic hygroscopic nature, acidity, intrinsic instability, and non-uniform coating. On the other hand, self-assembled monolayers (SAMs) have demonstrated better stability and higher device performance. Nevertheless, challenges persist, such as non-uniform coating and the hydrophobicity, when perovskite’s layers were fabricated on the top of SAMs. Inorganic hole transport layers like NiO can offer better stability and higher performance compared to organic HTLs, but surface defect-related undesirable reactions have been reported. In this study, an ultra-thin NiO (4nm) using atomic layer deposition (ALD) was applied, forming an ALD-NiO/SAMs bi-layer HTL. The use of ALD-NiO showed superior uniformity compared to traditional sol-gel and nano-particulate films’ preparation methods, ensuring uniformly formed bi-layers with SAMs. Together with bi-layer strategy, perovskite composition engineering and defect suppression were also conducted. The molecules with both electron donating cation and pseudo halide anion, pyridinium tetrafluoroborate (PyBF₄), were added into perovskite precursor solution to suppress defects in perovskite layers. The suppressed defect was analyzed with thermal admittance spectroscopy. Finally, i-PSCs based on the bi-layer of ALD-NiO/SAMs with defects suppressed perovskite layers demonstrated high power conversion efficiency of 24.0%.