Perovskite solar cells (PSCs) have appeared as a promising design for next-generation thin-film photovoltaics because of their cost-efficient fabrication processes and excellent optoelectronic properties. However, PSCs containing a metal oxide compact layer (CL) suffer from poor long-term stability and performance. The quality of the underlying substrate strongly influences the growth of the perovskite layer. In turn, the perovskite film quality directly affects the efficiency and stability of the resultant PSCs. Thus, substrate modification with metal oxide CLs to produce highly efficient and stable PSCs has drawn attention. In this review, metal oxide-based electron transport layers (ETLs) used in PSCs and their systemic modification are reviewed. The roles of ETLs in the design and fabrication of efficient and stable PSCs are also discussed. This review will guide the further development of perovskite films with larger grains, higher crystallinity, and more homogeneous morphology, which correlate to higher stable PSC performance. The challenges and future research directions for PSCs containing compact ETLs are also described with the goal of improving their sustainability to reach new heights of clean energy production.

A nickel oxide (NiO _x ) hole transport layer was made from nickel oxide powder by a simple process and non-stabilizer or chelating agent. We used ethanol as the main solvent and less than 2% nitric acid as the co-solvent. The formation reaction mechanism of the NiO _x thin film was also studied. Perovskite solar cells (PSCs) with an optimum thickness of 70 nm exhibited a power conversion efficiency as high as 12.99%, which is superior to those of PSCs with their counterparts. The moisture stability of NiO _x-based devices (non-encapsulated) remained above 70% of their initial output after 700 h storage at ambient conditions.

The availability of low-cost hole transport materials (HTMs) that are easy to process is crucial for the eventual commercialization of perovskite solar cells (PSCs), as the commonly used HTM (Spiro-OmeTAD) is expensive, and its processing is complex. In this study, we synthesized an amorphous molecular material (termed as TPA-glass) from the condensation of 2-mexylamino-4-methylamino-6-(4-aminophenylamino)-1,3,5-triazine and N-(4-formylphenyl)diphenylamine with a low-cost and easy process, and applied as an HTM in PSCs. We investigated the effect of TPA-glass thin-films with varying thickness, as well as their corresponding solar cell’s properties. The preliminary performance data indicate that TPA-glass thin-film can be a potential HTM candidate for planar PSCs.