Low-Pb Substitution Unlocks Cd-Based Ruddlesden–Popper Perovskites for Bright Emission and Ambipolar Transport

Two-dimensional (2D) Ruddlesden–Popper (RP) Cd-based perovskites have attracted increasing interest in optoelectronics owing to their environmental stability and tunable structural dimensionality. However, strong excited-state localization, abundant deep-level trap states, and inefficient carrier transport limit emission efficiency and device performance. Here, we report low-Pb-substituted 2D RP Cd-based perovskites, (PA)2CsCd2–xPbxCl7 (x = 0–0.4), and demonstrate that partial Pb2+ substitution provides an effective route to concurrently regulate luminescence and charge transport. At the optimal Pb2+ substitution level of x = 0.2, the photoluminescence quantum yield increases by approximately 7.6-fold, rising from 10.5% for the pristine sample to 80%. Steady-state and time-resolved photoluminescence analyses indicate a gradual redistribution from long-lived self-trapped exciton emission toward faster, higher-energy excitonic recombination. Field-effect transistors based on (PA)2CsCd1.8Pb0.2Cl7 exhibit pronounced ambipolar transport, with median hole and electron mobilities of 3.62 cm2 V–1 s–1 and 1.81 cm2 V–1 s–1, respectively, and a high on/off ratio of 8 × 107. Density functional theory calculations further reveal that Pb2+ substitution modulates the band-edge electronic states and suppresses the formation of deep-level defects. This work indicates that low-level Pb2+ substitution is an effective route for the concurrent optimization of luminescence and charge transport in Cd-based 2D perovskites, highlighting their potential for applications in high-performance transistors and light-emitting devices.