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

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 (Jsc) 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 Jsc 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.