Improving the stability and efficiency of polymer solar cells by γ-radiated graphitic carbon nitride

Graphitic carbon nitride (g-C3N4) is a potential additive that can alter the polymer solar cells (PSC) performance. Hereby, we report a novel strategy by applying gamma-radiated g-C3N4 as additive into bulk heterojunction polymer solar cell (BHJ-PSC). The incorporation of gamma-radiated g-C3N4 into the active layer P3HT:PC61BM augments the efficiency of BHJ-PSC by more than half with respect to the standard undoped device counterpart. The increased performance of gamma-radiated g-C3N4-doped BHJ-PSC is related to increased surface roughness, higher crystallinity, greater optical absorption of the polymer layer and improved charge transfer/recombination dynamics within the device. The optimized BHJ-PSC containing gamma-radiated g-C3N4 without encapsulation reaches 2.4% power conversion efficiency (PCE) and the device also retains 60% of the initial PCE even after exposure to high humidity condition (relative humidity 40%-70%) for 30 days. This suggests that gamma-radiated g-C3N4 is capable of preventing moisture and oxygen-induced degradation of P3HT:PC61BM. The gamma-radiated g-C3N4 additive is also employed in PBDTTT-C:PCBM polymer system which demonstrates the champion PCE of 2.9%. The present work not only provides an effective strategy for simultaneously enhancing the efficiency and stability of BHJ-PSC, but also opens up a new horizon for radiation technology and additive engineering.