Thickness Insensitive UV Blocking Layer Meliorating Carrier Extraction and Deep Trap towards Stable Organic Solar Cells

Abstract The photostability of organic solar cells (OSCs) is extremely crucial to their commercial application. Herein, double‐layered anode interface layer (DL‐AIL) with ultraviolet (UV) absorber BP2 is constructed by layer‐by‐layer processing to simultaneously improve power‐conversion efficiencies (PCEs) and photostability of OSCs. The DL‐AIL exhibits good UV absorbance and photon utilization due to the effective Förster energy transfer from BP2 to polymer donor. High electric conductivity, optimal work function, and improved surface roughness can be obtained as well. The DL‐AIL based devices also achieve higher PCEs with excellent thickness insensitivity, attributed to the remarkable increase on electric conductivity of DL‐AIL and reduced transport resistance. More intriguingly, even under irradiation in air by xenon lamp with UV band, an extrapolated T₈₀ lifetime of the device based on DL‐AIL with 85 nm thick can reach 1306 h, which is approximately 54 times of that of PEDOT:PSS based device. Furthermore, the degradation mechanism of OSCs with different AIL is revealed by transient charge extraction, capacitance‐voltage and capacitance‐frequency. The incorporation of BP2 layer delivers improved charge carrier density and constrained deep trap in the aged devices. Consequently, this new finding demonstrates that the DL‐AIL strategy can promote the efficiency and long‐term stability of OSCs.