image: a Schematic illustration of the device configuration of planar Sb2S3 solar cells. b Band alignment of the components of Sb2S3 solar cells. c J-V curves of best-performing control and MEA-Sb2S3 solar cells, measured under 1-sun (AM1.5G, 100 mW cm-2) illumination. d EQE spectra of the control and MEA-4 Sb2S3 solar cells. e-h Statistics of the performance parameters of the control and MEA-Sb2S3 devices obtained with the addition of different concentrations of MEA.
Credit: Xiao Chen et al.
The rapid development of IoT technologies is leading to an ongoing exponentially growing market of smart devices. Currently, autonomous IoT nodes are mostly powered using batteries. However, the short lifespan of batteries not only limits the power consumption and size of IoT devices, but also restricts the applications to the cases which are compatible with battery replacement and maintenance. Indoor photovoltaics (IPVs), which capture energy from ambient lighting (either from artificial light sources, or daylight), have significant potential to provide sustainable power for driving wireless IoT nodes that communicate using a range of protocols, such as Bluetooth low energy, RFID tags, LoRa, passive Wi-Fi, Zigbee, ANT, etc. The narrow emission spectra of indoor light sources (e.g., WLEDs and fluorescent lamps (FLs)) range from 400 to 700 nm, which determines the optimal bandgap for indoor light-absorbing materials to be around 1.80-2.00 eV. Sb2S3 is an earth-abundant, low-toxicity and stable material with a bandgap of ~1.75 eV, close to the optimal bandgap value for IPV applications. According to calculations by Hoye et al., the spectroscopic limited maximum efficiency (SLME) reaches 47% under 1000 lux white LED lighting. However, up to now, the performance of Sb2S3 solar cells still lags far behind the theoretical efficiency and requires further improvements.
In a new paper published in Light Science & Application, a team of scientists, led by Professor Ru Zhou, from School of Electrical Engineering and Automation, Hefei University of Technology, and co-workers have developed an additive engineering strategy for high performance Sb2S3 indoor photovoltaics. The addition of monoethanolamine (MEA) into the precursor solution allows the nucleation and growth of Sb2S3 films to be controlled, enabling the deposition of high-quality absorbers with reduced grain boundary density, optimized band positions and increased carrier concentration. Complemented with computations, it is revealed that the incorporation of MEA leads to a more efficient and energetically favorable deposition for enhanced heterogeneous nucleation on the substrate, which increases the grain size and accelerates the deposition rate of Sb2S3 films. Due to suppressed carrier recombination and improved charge-carrier transport in Sb2S3 absorber films, the MEA-modulated Sb2S3 solar cell yields a power conversion efficiency (PCE) of 7.22% under AM1.5G illumination, and an IPV PCE of 17.55% under 1000 lux WLED illumination, which is the highest yet reported for Sb2S3 IPVs. Furthermore, we construct high performance large-area Sb2S3 IPV minimodules to power IoT wireless sensors, and realize the long-term continuous recording of environmental parameters under WLED illumination in an office. This work highlights the great prospect of Sb2S3 photovoltaics for indoor energy harvesting.
“Crystalline silicon (c-Si), which dominates the outdoor PVs market, would not be well suited for indoor energy harvesting, due to its small bandgap (~1.12 eV). The state-of-the-art commercial solution up to now for IPVs is hydrogenated amorphous silicon (a-Si:H), however the PCEs of commercially available standard a-Si:H module devices typically only range from 4.4% to 9.2%. In this work, Sb2S3 solar cells we obtained deliver an impressive IPV efficiency of 17.55% under 1000 lux WLED illumination.”
“Having developed efficient Sb2S3 IPVs, we are in the position to prototype these for powering IoT wireless electronics. We successfully constructed an IPV minimodule based on Sb2S3 devices and successfully reported the use of this module to power IoT wireless devices for the first time.” They added.
“IPVs are deployable in view of their reliance on radiative energy transfer and indoor lighting being ubiquitously available and predictable. Furthermore, IPVs afford relatively high energy density compared to other ambient energy harvesting technologies. Therefore, the development of high performance IPVs is important for sustainable IoT applications. This work demonstrates the broad prospect of environment friendly Sb2S3 absorber materials for IPV applications.” The scientists forecast.
Article Title
Additive engineering for Sb₂S₃ indoor photovoltaics with efficiency exceeding 17%