Enhancing the short-circuit current and power conversion efficiency of polymer solar cells with graphene quantum dots derived from double-walled carbon nanotubes

Abstract

Derived from double-walled carbon nanotubes, graphene quantum dots (GQDs) with a uniform size distribution were prepared through solution chemistry. The GQDs in chlorobenzene exhibited bright blue emission upon UV excitation. The introduction of the GQDs into a bulk heterojunction polymer solar cell based on poly(3-hexylthiophene):(6,6)-phenyl-C61 butyric acid methyl ester (P3HT:PCBM) resulted in a significant enhancement of the power conversion efficiency (PCE). The efficiency was further improved by adjusting the PCBM content in the active layer, reaching a maximum PCE of 5.24%. This ternary system based on blended P3HT:PCBM:GQDs represents a new method to enhance the efficiency of polymer solar cells. Fushan Li, Tailiang Guo and co-workers from Fuzhou University, China, have constructed an efficient polymer solar cell by adding graphene quantum dots to a conventional design. Lighter than their silicon-based counterparts, easier to fabricate and more environmentally friendly, polymer solar cells show particular promise but do not yet convert enough of the sunlight they absorb for practical application. The active layer of such solar cells comprises an electron-donating material — often the conjugated polymer poly(3-hexylthiophene) — and an electron-accepting one, such as a fullerene derivative. The use of graphene quantum dots as the electron acceptor has recently been shown to endow a photovoltaic device with good stability and low cost but also a relatively poor performance. Li, Guo and their colleagues have now incorporated graphene quantum dots — prepared from double-walled carbon nanotubes — in addition to, rather than instead of, the fullerene-based electron acceptor of a polymer solar cell, significantly enhancing its energy conversion efficiency. Graphene quantum dots (GQDs) derived from double-walled carbon nanotubes with strong emission were prepared through solution chemistry. The introduction of GQDs in a bulk heterojunction polymer solar cell based on Poly (3-hexylthiophene):(6,6)-phenyl-C61 butyric acid methyl ester (P3HT:PCBM) resulted in the significant enhancement of power conversion efficiency (PCE). The efficiency can be further improved by adjusting the PCBM content in the active layer, with the highest PCE of 5.24%.