Silver antimony sulfide (AgSbS₂) has recently emerged as a promising semiconducting material for application in optoelectronics. Its nontoxicity, earth-abundant composition, high absorption coefficient, phase, and environmental stability make it particularly interesting for photovoltaic applications. This study presents a facile room-temperature synthesis of colloidal AgSbS₂ nanocrystals via cation exchange. The obtained AgSbS₂ nanocrystals show a unique postsynthetic size tunability with tunable optoelectronic properties while maintaining an ideal elemental composition. The great potential of these ternary nanocrystals is demonstrated by their integration into planar nanocrystal solar cells for the first time, in which the AgSbS₂ nanocrystals form a compact layer, reaching a promising power conversion efficiency of up to 1.99%, approaching the performance of bulk AgSbS₂ photovoltaic cells.