Abstract
Although power conversion efficiencies of organic-inorganic lead halide perovskite solar cells (PSCs) are approaching those of single-crystal silicon solar cells, the working device stability due to internal and external factors, such as light, temperature, and moisture, is still a key issue to address. The current world-record efficiency of PSCs is based on organic hole transport materials, which are usually susceptible to degradation from heat and diffusion of dopants. A simple solution would be to replace the generally used organic hole transport layers (HTLs) with a more stable inorganic material. This review article summarizes recent contributions of inorganic hole transport materials to PSC development, focusing on aspects of device performance and long-term stability. Future research directions of inorganic HTLs in the progress of PSC research and challenges still remaining will also be discussed.
Highlights
Nickel oxide has already been used in dye-sensitized solar cells (DSSCs) and organic photovoltaics (OPV) as the p-type hole transport layers (HTLs) before being applied in perovskite solar cells (PSCs) [62,63]
CuS nanoparticles were coated on top of indium tin oxide (ITO) in a p-i-n configuration configuration PSCs, which resulted in a power conversion efficiencies (PCEs) of 16.2% [50], and maintained over 90%
cobalt oxide (CoOx) spin-coated on top of ITO in a p-i-n configuration resulted in a PCE of 14.5% [51]
Summary
(iii) exhibit a wide optical bandgap so that there will be no contribution as a second light absorber layer, (iv) possess high transparency to minimize optical losses, (v) show adequate hydrophobic nature to tolerate long-term exposure to humidity, (vi) have low materials and fabrication costs, (vii) be environmentally friendly, and (viii) show good stability against light and heat [10,11,12]. While much effort has been made to modify the perovskite layer to enhance device stability [13,14,15,16], another straightforward approach to enhance the working stability of PSCs would be to replace these organic HTLs with inorganic materials.
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