Balancing Light Absorptivity and Carrier Conductivity of Graphene Quantum Dots for High-Efficiency Bulk Heterojunction Solar Cells

Abstract

Graphene quantum dots (GQDs) have been considered as a novel material because their electronic and optoelectronic properties can be tuned by controlling the size and the functional groups of GQDs. Here we report the synthesis of reduction-controlled GQDs and their application to bulk heterojunction (BHJ) solar cells with enhanced power conversion efficiency (PCE). Three different types of GQDs--graphene oxide quantum dots (GOQDs), 5 h reduced GQDs, and 10 h reduced GQDs--were tested in BHJ solar cells, and the results indicate that GQDs play an important role in increasing optical absorptivity and charge carrier extraction of the BHJ solar cells. The enhanced optical absorptivity by rich functional groups in GOQDs increases short-circuit current, while the improved conductivity of reduced GQDs leads to the increase of fill factors. Thus, the reduction level of GQDs needs to be intermediate to balance the absorptivity and conductivity. Indeed, the partially reduced GQDs yielded the outstandingly improved PCE of 7.60% in BHJ devices compared to a reference device without GQDs (6.70%).

Efficiency Enhancement of Silicon Heterojunction Solar Cells via Photon Management Using Graphene Quantum Dot as Downconverters

“…Graphene quantum dots (GQDs), exhibiting unique semiconducting properties, 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 5 have becoming a newly emerged material for optoelectronic applications. 11,12 The bandgap of GQDs can be tuned by adjusting their chemical functional groups. 12 Additionally, the most intriguing feature of GQDs for optical applications is the photon downconversion property, which enables them to absorb photons in shorter wavelength regions and then emit photons in longer wavelength regions.…”

Graphene quantum dots: In the crossroad of graphene, quantum dots and carbogenic nanoparticles

“…Partially reduced GQDs derived by graphite oxide dots were found to exhibit optimal performance compared to their highly oxidized and fully reduced counterparts [49] . This behavior indicates that the overall performance reflects an interplay between enhanced light absorptivity in the highly oxidized particles that increases Jsc and improved conductivity in the fully reduced particles that increases the fill factors (FF).…”

Graphene-based materials for polymer solar cells

“…After incorporating the GQDs into the active layer of P3HT:PCBM-based PSCs, a considerable increase of PCE was achieved compared with the conventional device without GQDs, producing a PCE of 5.24 %. Kim et al [73] utilized reduction-controlled GQDs (GOQDs), which were blended with efficient active layer of polymer thieno [3,4-b]thiophene/benzodithiophene (PTB7):PC 71 BM, to increase the optical absorptivity and charge carrier extraction of PSCs (Fig. 16C).…”

“…A c c e p t e d M a n u s c r i p t Although the aforementioned work has partly addressed some issues of graphene-based materials used in the active layers of PSCs, including the dispersion in the organic solvent [65][66][67][68], the optimization of electron transport between donors and acceptors [72] and improvement of the optical utilization in active layer [73]. However, the overall performance of those devices using graphene-based materials in active layer is still poorer than that of conventional PSCs using C 60 and its derivatives and graphene-based materials cannot be used as effective electron acceptors to replace C 60 derivatives for highly efficient PSCs.…”