Carbon-based materials for stable, cheaper and large-scale processable perovskite solar cells

Abstract

Almost ten years after their first use in the photovoltaic (PV) field, perovskite solar cells (PSCs) are now hybrid devices that, in addition to having reached silicon performance, can accelerate the energy transition and boost the use of abundant elements for their manufacturing process. However, noble metals (in particular gold) represent the most typically used sources for back electrode fabrication, and this issue has been intensively considered by the research community in the last five years. This review shows how the most promising solution, considering also the need to develop a large-scale production process, is based on the use of carbon-based materials for the preparation of back electrodes. Graphite, carbon black, graphene and carbon nanotubes (CNTs) have been proposed, functionalized and characterized, leading to laboratory-scale solar cells and modules capable of providing excellent efficiencies and ensuring stability greater than those of gold-based devices. Strengthened by these results and its hydrophobizing properties, carbon has also started to be used as an electron transporting material (ETM), with excellent results on both rigid and flexible substrates. This review discusses the major advances and the updated state-of-the-art in the carbon-based PSC scenario, keeping a solid trajectory where the accessibility, low cost, high electrical conductivity, chemical stability and controllable porosity of carbon are highlighted and exploited in the design of upscalable hybrid solar cells. Broader contextToday, more than 75% of the world energy demand is met by traditional, non-sustainable energy resources, mainly based on coal, natural gas and oil. Photovoltaics represents a concrete action to mitigate fossil fuel consumption, and among all the developed solar cells, perovskite-based ones have shown the highest increase in terms of efficiency (currently above 25%). Halide perovskites, as a family of new-generation semiconductor materials, are also exploitable for light-emitting devices, photodetectors and memristors, but their use in photovoltaics gives rise to outstanding performances. Here, photogenerated charges pass through electron/hole transporting materials and are transferred to the external circuit by front and back electrodes. While the front electrode is a common conductive glass, many issues are now under study concerning the back electrode, traditionally made of gold. Indeed, replacing this expensive metal with a much cheaper alternative is vital for realizing affordable solar technologies. Carbon, in its multiple forms, represents the winning solution and the scientific community has recently shown its large scale processability, its power as a stability booster and some interesting effects at the perovskite/electrode interface. This review shows how carbon is becoming the winning ingredient for the scaling up and worldwide diffusion of perovskite solar cells.

Multi-component engineering to enable long-term operational stability of perovskite solar cells

“…The advantage of the triple-layer carbon based mesoscopic PSCs is their lost-cost process avoiding the use of hole transporting layer and noble metals like Au and Ag, together with the exceptional long-term stability. Nevertheless, the efficiency of this type of PSC still falls far behind the hybrid PSCs (< 17%) [50], which is mainly due to the poor contact at the perovskite/carbon interface, and the relatively high resistance of bulk carbon [51]. A good interface contact is depending on the porosity and wettability of carbon, which enables the diffusion and loading of perovskite into the porous structure.…”

Reducing Agents for Improving the Stability of Sn‐based Perovskite Solar Cells

“…Recently, large‐area fabrication techniques for transport materials, perovskite absorbers and counter electrodes are also developing rapidly. The improvement in spray deposition, blade coating, slot‐die coating and inkjet printing methods make it potential for the scalable fabrication of perovskite PV. However, these highly efficient PSCs all contain Pb that is toxic and soluble in water.…”

Effect of UV-Light Treatment on Efficiency of Perovskite Solar Cells (PSCs)

“…Despite performing the PSC fabrication process in a well-controlled glove box under low-level humidity, moisture, and oxygen, defects and poor adhesion between layers appeared [9,10]. Moreover, after a compact TiO 2 layer and a mesoporous TiO 2 layer were deposited on the FTO electrode, the temperature increased to over 450 • C. Therefore, to achieve a high energy conversion performance of PSCs, the layers should be smooth and uniform [11][12][13].…”

“…Unfortunately, all UV light is not helpful to humans, and UV-A and UV-B are related to skin cancer [14]. Among them, UV-C Energies 2020, 13 is used to remove impurities on the surface by induced ozone (O 3 ) in the air. Some research groups have tried to enhance the power conversion efficiency (PCE) of solar cells [15,16].…”