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Tunneling enhancement of cell performance in InGaAs/GaAsP multiple quantum well (MQW) solar cells has been studied to investigate the potential in overcoming the carrier collection problem, which hinders the maximum performance of quantum structure solar cells. To accurately investigate the effects of the tunneling effect, the study was carried out in samples with different GaAsP barrier thickness, controlled absorption edge, and constant built-in field. The tunneling effect has been confirmed by evaluating carrier escape times using the time-resolved photoluminescence technique and measuring carrier collection efficiency at various temperatures. The collection efficiencies at low temperature are found to be remarkably improved when barrier thickness was below 3 nm, which can be regarded as the critical thickness for efficiently facilitating tunneling enhancement. It can also be concluded that the carrier transport model based on thermal and tunneling processes is practical enough to describe most of the carrier sweep-out dynamics in MQW solar cells.