Vertically Oriented BiI₃ Template Featured BiI₃/Polymer Heterojunction for High Photocurrent and Long-Term Stable...

Nontoxic and stable materials are one of the necessities for commercialization of solar devices. However, most lead-free absorbers have limited light absorption range as well as poor morphology. In this work, a vertically oriented BiI₃ template induced by Li-bis(trifluoromethanesulfonyl)imide dopant is intimately integrated with a light-absorbing polymer to form an organic-inorganic BiI₃/polymer heterojunction absorber in solar cells. Compared with the dopant-free BiI₃/polymer, the broadened light absorption of the doped BiI₃/polymer enhances the external quantum efficiency (EQE) of the device beyond 500 nm as well as extends the EQE edge from 650 to 750 nm, which significantly increases the short-circuit current (J_sc) of the device from 1.3 to 3.7 mA cm^-2. The polymer top layer is further optimized to improve charge extraction, which achieved the highest J_sc recorded (7.8 mA cm^-2) for BiI₃-based solar cells and an efficiency of 1.03%. Moreover, the encapsulated device shows no degradation after storing in ambient conditions for nearly 2 years.