Wireless sensor networks can potentially achieve perpetual maintenance-free operation by harnessing ambient energy from the environment. However, most environmental energy sources, such as vibrations, heat, radio frequency (RF) are usually inadequate and sporadic in nature. Therefore, sensor nodes that rely solely on such environmental resources, suffer from frequent and random energy outages. This energy outage leads to intermittent connectivity and induces a large delay in multi-hop transmission paradigms. The objective of this research is to minimize the end-to-end latency due to this intermittent connectivity. In order to address this problem, several approaches are explored. First, cooperative relaying is investigated as a potential mechanism for reducing the transmission delay. The latency associated with cooperative relaying over unicast routes is analyzed and a novel scheme is proposed to improve the performance of cooperative relaying in a more practical multi-hop setting. Next, a predictive retransmission strategy is developed to find the best retransmission intervals that maximize the success probability associated with each transmission. This strategy is then adapted to two different asynchronous routing protocols: cooperative relaying over unicast routes and opportunistic routing. Finally, the delay characteristics of RF energy harvesting sensor networks is explored and analytical models are formulated to reduce delay by efficiently distributing packet forwarding load between the transmitter and receiver nodes. Performance evaluations from the theoretical models and simulations show that the proposed methods can significantly improve the delay performance in comparison to existing solutions.