Improved size distribution of AgBiS₂ colloidal nanocrystals by optimized synthetic route enhances photovoltaic performance

Ternary silver bismuth sulfide (AgBiS₂) colloidal nanocrystals (NCs) have been recognized as a photovoltaic absorber for environmentally-friendly and low-temperature-processed thin film solar cells. However, previous synthetic methods involving hot injection of sulfur precursors into metal oleate precursor solutions do not provide a balance between nucleation and growth, leading to AgBiS₂ NCs with broad size distributions. Here, we demonstrate the modified synthetic route that size distribution of AgBiS₂ NCs can be improved by pre-adding the non-coordinating 1-octadecene (ODE) solvent into metal precursor solutions, leading to controlled concentration of coordinating oleic acid with improved hot-injection synthetic conditions. The addition of ODE as a non-coordinating solvent to metal precursor/oleic acid solution significantly suppresses variations in the concentration of coordinating oleic acid after injection of the sulfur precursor solution, leading to a homogenous reaction between the metal and sulfur precursors. For photovoltaic devices fabricated using the resultant AgBiS₂ NCs, the champion device shows power conversion efficiency (PCE) of 5.94% with an open-circuit voltage (V_OC) of 0.52 V. This performance is better than that a control device (PCE of 5.50% and V_OC of 0.49 V) because of the reduced energetic disorder and band tail broadening originating from the uniformly-sized AgBiS₂ NCs.