Recent advances of graphene-based materials in planar perovskite solar cells

Perovskite solar cells (PSC) have emerged as highly efficient photovoltaic devices, boasting remarkable power conversion efficiencies (PCE) exceeding 25.5%. However, the incorporation of perovskite films raises environmental concerns due to associated toxicity, and PSC deteriorates over time due to material breakdown accelerated by heat, moisture, and undesired chemical reactions at interfaces. For example, employing titanium dioxide TiO₂ as the electron transport layer (ETL) and the organic semiconductor Spiro-OMeTAD as the hole transport layer (HTL) can lead to instability in the device. The broad bandgap of TiO₂ leads to charge carrier recombination in ETL, undermining device performance, along with the high cost and complex synthesis of Spiro-OMeTAD. Researchers have investigated several methods to tackle these challenges, including altering the interfacial structure and employing adaptable materials between the charge-gathering electrode and perovskite active layers. Due to their extensive bandgap and notable electron mobility, perovskite oxides are highly attractive; however, these materials encounter difficulties such as clustering, which can cause short circuits and leakage current. They also suffer from inefficient charge separation, surface hydrophilicity, and inadequate absorption of visible light. Furthermore, the addition of graphene particles to both compact and mesoporous TiO₂ layers, which act as electron-selective layers, aims to lower series resistance and boost electron extraction efficiency, achieving a peak PCE of 26.3%. These materials have garnered attention for their outstanding optoelectronic properties, superior stability, and non-toxic characteristics. This review extensively delves into the integration of graphene-based materials as interfacial layers and how that will affect the performance of PSC in terms of stability and efficiency.