A collaborative effort by researchers from the Centre for Hybrid and Organic Solar Energy (CHOSE), Department of Electronic Engineering at Tor Vergata University of Rome, Italy, the Department of Textile Engineering at the University of Guilan, Iran, GreatCell Solar Italia, Institute of Crystallography (IC-CNR), Italy, Department of Biological and Environmental Sciences and Technologies at the University of Salento, Italy and Institute of Nanotechnology (CNR NANOTEC), Italy, has resulted in the development of flexible perovskite solar cells with remarkable power conversion efficiencies (PCE) under white LED illumination.
The team achieved a maximum PCE of 28.9% at an illuminance of 200 lx and a record of 32.5% at 1000 lx, essentially converting a third of the incoming power (note that under 1 sun this figure for perovskite technology is less, i.e. one quarter).
The researchers believe this represents the highest reported efficiency ever achieved on polyethylene terephthalate (PET) films at illuminance levels found in environments like supermarkets, where it could be used to power smart labels and sensors.
The film is only about an eighth of a mm thick, so the cells are flexible and can be curved easily for adaptation to many surfaces.
PET is a widely used recyclable plastic that is also used in packaging, but in film form has become the transparent polymer substrate of choice for plastic electronics. In fact, compared to alternative materials like PEN it is much cheaper (even by a factor 6) as well as more stable to UV radiation.
The impressive performance under indoor lighting was achieved through a dual low-temperature approach of compositional engineering, where some of the iodine (I) in the perovskite was replaced with bromine (Br), to increase the bandgap of the perovskite to better match the visible light spectrum of white LEDs.
Additionally, interface modification was implemented using a molecule, i.e. tetrabutylammonium bromide (TBAB), to create a low-dimensional perovskite phase at the top of the perovskite film. These strategies resulted in a 42% improvement in efficiency through perovskite composition engineering, and an additional 26% enhancement with the TBAB interlayer.
The introduction of the low-dimensional perovskite phase reduced the density of defects and minimized leakage currents, leading to improved charge carrier lifetimes, which is especially crucial under low light levels commonly encountered indoors.
The research findings have demonstrated the promising potential of these flexible perovskite solar cells for indoor energy harvesting applications. All layers of the cells, except for the two electrodes, were solution processed at low temperatures (maximum 100 °C), making the technology easy to integrate with other printed electronic components on the same substrate, and compatible with low-cost manufacturing.
Ambient indoor conditions represent a milder environment compared to stringent outdoor conditions suggesting an initial commercial outlet which is much less taxing on device lifetimes for this technology. Thus, the researchers suggest that the excellent performance demonstrated gives these devices a new competitive attribute that can pave the way for perovskite solar cells to contribute to energy harvesting and the powering of the indoor electronics of the future, including the fast-rising markets of autonomous indoor wireless sensor networks, smart buildings, portable, wearable, and the IoT electronics.
