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

Abstract

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 (VOC) of 0.52 V. This performance is better than that a control device (PCE of 5.50% and VOC of 0.49 V) because of the reduced energetic disorder and band tail broadening originating from the uniformly-sized AgBiS2 NCs. © 2020 John Wiley & Sons Ltd