Tin-Based Perovskite Solar Cells Reach Over 13% with Inclusion of N-Doped Graphene Oxide in Active, Hole-Transport, and Interfacial Layers

Tin-based perovskite (Sn-PS) is one of the most promising candidates in lead-free perovskite solar cells (PSCs), but its poor stability and low power conversion efficiency (PCE) have been the main bottleneck towards further development. Here, to develop a stable and efficient Sn-based PSC, nitrogen-doped graphene oxide (N_xGO) has been, for the first time, incorporated in active, hole-transport and interfacial layers. The inclusion of N_xGO slowed the crystallization of Sn-PS and suppressed the Sn²⁺/Sn⁴⁺ oxidation, resulting in pinhole-free dense films having large grains, reduction of recombination loss, well-matched energy levels, and thereby significantly improving the device performance. Compared to the pristine Sn-PS cells, the champion devices with N_xGO-based composites in active, hole-transport, and interfacial layers showed dramatic enhancement of photovoltaic parameters (i.e., open-circuit voltage = 0.961 V, photocurrent = 21.21 mA cm⁻², fill factor = 65.05% and PCE = 13.26%). Furthermore, the N_xGO-based cells without encapsulation showed remarkable improvement of long-term stability with sustaining 91% of the initial PCE over 60 d, photostability, and reproducibility.