Performance Comparison between the Nanoporous NiO x Layer and NiO x Thin Film for Inverted Perovskite Solar Cells with Long-Term Stability

Metal organic framework derived NiO x nanoparticles for application as a hole transport layer in perovskite solar cells

NiO _x as a hole transport layer (HTL) has gained a lot of research interest in perovskite solar cells (PSCs), owing to its high optical transmittance, high power conversion efficiency, wide band-gap and ease of fabrication. In this work, four different nickel based-metal organic frameworks (MOFs) using 1,3,5-benzenetricarboxylic acid (BTC), terephthalic acid (TPA), 2-aminoterephthalic acid (ATPA), and 2,5-dihydroxyterephthalic acid (DHTPA) ligands respectively, have been employed as precursors to synthesize NiO _x NPs. The employment of different ligands was found to result in NiO _x NPs with different structural, optical and morphological properties. The impact of calcination temperatures of the MOFs was also studied and according to field emission scanning electron microscopy (FESEM), all MOF-derived NiO _x NPs exhibited lower particle size at lower calcination temperature. Upon optimization, Ni-TPA MOF derived NiO _x NPs calcined at 600 °C were identified to be the best for hole transport layer application. To explore the photovoltaic performance, these NiO _x NPs have been fabricated as a thin film and its structural, optical and electrical characteristics were analyzed. According to the findings, the band energy gap (E _g) of the fabricated thin film has been found to be 3.25 eV and the carrier concentration, hole mobility and resistivity were also measured to be 6.8 × 10¹⁴ cm^-3; 4.7 × 10¹⁴ Ω cm and 2.0 cm² V^-1 s^-1, respectively. Finally, a numerical simulation was conducted using SCAPS-1D incorporating the optical and electrical parameters from the thin film analysis. FTO/TiO₂/CsPbBr₃/NiO _x /C has been utilized as the device configuration which recorded an efficiency of 13.9% with V _oc of 1.89 V, J _sc of 11.07 mA cm^-2, and FF of 66.6%.

Preparation of Nickel Oxide Nanoflakes for Carrier Extraction and Transport in Perovskite Solar Cells

Hole transport layers (HTLs) with high conductivity, charge extraction ability, and carrier transport capability are highly important for fabricating perovskite solar cells (PSCs) with high power conversion efficiency and device stability. Low interfacial recombination between the HTL and perovskite absorber is also crucial to the device performance of PSCs. In this work, we developed a three-stage method to prepare NiO_x nanoflakes as the HTL in the inverted PSCs. Due to the addition of the nanoflake layer, the deposited perovskite films with larger grain sizes and fewer boundaries were obtained, implying higher photogenerated current and fill factors in our PSCs. Meanwhile, the downshifted valence band of the NiO_x HTL improved hole extraction from the perovskite absorber and open-circuit voltages of PSCs. The optimized device based on the NiO_x nanoflakes showed the highest efficiency of 14.21% and a small hysteresis, which outperformed the NiO_x thin film as the HTL. Furthermore, the device maintained 83% of its initial efficiency after 60 days of storage. Our results suggest that NiO_x nanoflakes provide great potential for constructing PSCs with high efficiency and long-term stability.

Efficient and stable perovskite solar cells using manganese-doped nickel oxide as the hole transport layer

The device based on a Mn-doped NiOx HTL retained 70% of its initial efficiency after 35 days’ storage under a continuous halogen lamp matrix exposure.