In this paper, the performance of a co-operative device-to-device (D2D) network is investigated. All the D2D users sense the cellular user (CU) spectrum and use it in hybrid mode: underlay and overlay. The expressions of throughput and outage are developed under the considered network scenario. An algorithm is proposed to optimize the sensing time to minimize the outage. The performance is investigated in terms of throughput and outage for several network parameters such as a number of D2D users, sensing time, signal-to-noise ratio (SNR), allowable interference threshold, and CU transmit power. Sensing time is optimized to minimize the outage. The interference threshold and target rate have a significant impact on network performance. The network has to suffer outage for lower values of allowable interference threshold and higher values of the target rate. The impact of channel fading on the network performance is also studied. A simulation model is developed in MATLAB on the basis of the analytical development of the considered network model. © 2021 John Wiley & Sons Ltd.