Graphene and Carbon Quantum Dot-Based Materials in Photovoltaic Devices: From Synthesis to Applications

Abstract

Graphene and carbon quantum dots have extraordinary optical and electrical features because of their quantum confinement properties. This makes them attractive materials for applications in photovoltaic devices (PV). Their versatility has led to their being used as light harvesting materials or selective contacts, either for holes or electrons, in silicon quantum dot, polymer or dye-sensitized solar cells. In this review, we summarize the most common uses of both types of semiconducting materials and highlight the significant advances made in recent years due to the influence that synthetic materials have on final performance.

Keywords: carbon; graphene; photovoltaics; quantum dots; solar cells.

Figure 1

Illustration of CD (top) and GD (bottom) structures. Reproduced with permission of [12,13,14].

Figure 2

Schematic representation of both synthetic approaches. Reproduced with permission of [16].

Figure 3

Suzuki reaction followed to prepare graphene dots (described as product number 1 in the reaction scheme) from bromobenzoic acid. Reproduced with permission of [36]. Steps are as follows: (a) NaIO₄, I₂, concentrated H₂SO₄, room temperature; (b) Heated with diphenylphosphoryl azide in triethylamine and tert-butanol at 80 °C, followed by treatment with CF₃COOH in dichloromethane at room temperature; (c) Suzuki condition with 3-(phenylethynyl)phenylboronic acid, Pd(PPh₃)₄, K₂CO₃ in water, ethanol, and toluene mixture, 60 °C; (d) Iodine and tert-butyl nitrite in benzene, 5 °C to room temperature; (e) Suzuki condition with substituted phenyl boronic acid, Pd(PPh₃)₄, K₂CO₃ in water, ethanol, and toluene mixture, 80 °C; (f) Treatment with butyllithium in tetrahydrofuran (THF) at −78 °C, then with triisopropyl borate at −78 °C, followed by treatment with acidic water at room temperature; (g) Suzuki condition with 1,3,5-triiodobenzene, Pd(PPh₃)₄, K₂CO₃ in water and toluene mixture, 80 °C; (h) Tetraphenylcyclopentadienone in diphenylether, 260 °C; (i) FeCl3 in nitromethane and dichloromethane mixture, room temperature.

Figure 4

Schematic view of the obtention of CDs by electrochemical methods. Reproduced with permission of [28].

Figure 5

Estimated variation of the emission wavelength with the size for GDs. Reproduced with permission of [54].

Figure 6

Schematic representation of the composition and charge transfer processes in (a) DSSC [(1) light absorption; (2) electron injection; (3) electron collection; (4) reduction of the oxidized dye cation by the redox couple; (5) regeneration of the electrolyte at the counterelectrode] and (b) OSC [(1) Light absorption and creation of an exciton; (2) exciton diffusion; (3) exciton splitting at the interface; (4) diffusion and collection of charges]. Reproduced with permission of [61,65], respectively.

Figure 7

(a) Cross-sectional view of the SEM image; (b) JV curve of the devices comparing the effect of the insertion of the GDs. Reproduced with permission of [38].

Figure 8

Variation of the JV curve (a) and cell parameters (b) with increasing layers of CDs; Energy level alignments of the cells without (c) and with (d) CDs. Reproduced with permission of [30].

Figure 9

Energy band diagram showing possible paths for energy and charge transport and structure of the FTO/ZnS-CdS-ZnS/CDs/CuPc/S²⁻/MWCNT devices. Reproduced with permission of [33].