Additive engineering for Sb_2S_3 indoor photovoltaics with efficiency exceeding 17

Indoor photovoltaics (IPVs) have attracted increasing attention for sustainably powering Internet of Things (IoT) electronics. Sb_2S_3 is a promising IPV candidate material with a bandgap of  1.75 eV, which is near the optimal value for indoor energy harvesting. However, the performance of Sb_2S_3 solar cells is limited by nonradiative recombination, closely associated with the poor-quality absorber films. Additive engineering is an effective strategy to improved the properties of solution-processed films. This work shows that the addition of monoethanolamine (MEA) into the precursor solution allows the nucleation and growth of Sb_2S_3 films to be controlled, enabling the deposition of high-quality Sb_2S_3 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 Sb_2S_3 films. Due to suppressed carrier recombination and improved charge-carrier transport in Sb_2S_3 absorber films, the MEA-modulated Sb_2S_3 solar cell yields a power conversion efficiency (PCE) of 7.22 illumination, and an IPV PCE of 17.55 diode (WLED) illumination, which is the highest yet reported for Sb_2S_3 IPVs. Furthermore, we construct high performance large-area Sb_2S_3 IPV modules 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 Sb_2S_3 photovoltaics for indoor energy harvesting.