Suppression of PbI2 decomposition with Lewis base semicarbazide hydrochloride for photostable and efficient perovskite solar cells

Introducing excessive PbI2 in perovskite is widely used to fabricate high performance perovskite solar cells (PSCs) via two-step spin coating, whereas the photoinduced decomposition of excessive PbI2 may induce perovskite photodegradation for long-term illumination. In this work, a Lewis base semicarbazide hydrochloride (SH) is introduced in the first-step PbI2 film, which can anchor strongly PbI2 at the grain boundaries of perovskite, suppressing its photoinduced decomposition to Pb0 and I2, and consequently enhancing the long-term photostability of PSCs. In addition, it is verified that SH can also coordinate with the uncoordinated Pb2+ in perovskite, and thus stabilize [PbX6]4- octahedral to inhibit photoinduced ion migration. Therefore, the optimized PSC exhibits not only an improved power conversion efficiency (PCE) of 21.88%, but also an enhanced photostability with 82.8% of its initial PCE under 500 h continuous AM 1.5G illumination. This work provides a new strategy to suppress PbI2 photoinduced decomposition and perovskite photodegradation for the realization of photostable and efficient PSCs.