Expanding the Light Harvesting of CsPbI₂Br to near Infrared by Integrating with Organic Bulk Heterojunction for Efficient and Stable Solar Cells

All-inorganic perovskite (CsPbX₃, X = Br or I) solar cells demonstrate superior stability, while the power conversion efficiency (PCE) lags behind the organic-inorganic hybrid counterparts mainly due to the limitation of narrow absorption bands. To broaden their absorption spectrum and improve their PCE, all-inorganic perovskite/organic integrated solar cells utilizing CsPbI₂Br as an ultraviolet-visible light absorber and PBDTTT-E-T:IEICO as a near-infrared light absorber are demonstrated in this work. The integrated solar cells exhibit a broadened photoresponse to over 900 nm, attributed to the integration of PBDTTT-E-T:IEICO. The additional absorption enhances the short-circuit current density from 14.78 to 15.98 mA/cm², resulting in greatly improved PCE of 14.03% for integrated solar cells, much higher than that of the control perovskite solar cells (12.53%) and organic solar cells (7.51%). An in-depth understanding of the charge-transfer dynamic process in the CsPbI₂Br/PBDTTT-E-T:IEICO film is comprehensively analyzed by photoinduced transient absorption spectroscopy. Furthermore, the air stability and thermal stability of the integrated solar cells are greatly enhanced. For unencapsulated integrated solar cells, the PCE still preserves 95% of its initial value after aging for 300 h in an ambient environment and retains about 90% of its original value even after aging at 85 °C for 180 h in nitrogen.