With the goal of reducing solar energy costs further, new materials such as organic semiconductors are considered as a replacement for silicon. In this presentation, we will explore some fundamental properties of organic semiconductors that determine solar cell efficiency. Indeed, efficiency gains cannot be achieved without an in depth understanding of the underlying physics, the key to fine tweaking and optimization. In particular, we will determine how molecular arrangement, determined by “order” and “packing”, impacts the fate of charge transport. How ordered your desk is may influence how efficiently you work, and your state of mind. More importantly, however, is the way that folders are arranged (packed) on a desktop: files from the same projects are best placed together. The same idea holds true for organic semiconductors. Crystallinity (order) is an important lever to improve the efficiency of charge carriers traveling in the material, yet the way molecules pack in the crystalline phase is more important. We observe that, by tuning order and packing in organic semiconductors, the transport mechanism gradually evolves between two cases. Our results therefore provide guidelines for the design of new and efficient organic solar materials.