High Performance PbS Quantum Dot/Graphene Hybrid Solar Cell with Efficient Charge Extraction.

Byung-Sung Kim,Nanlin Zhang,Andrew A R Watt,Seungnam Cha,Bo Hou,Hazel E Assender,Jong Bae Park,Jung Inn Sohn,Yuljae Cho,John Hong,Sanghyo Lee,Darren C J Neo,Sangyeon Pak,Jong Min Kim

doi:10.1021/acsami.6b02544

Byung-Sung Kim, Nanlin Zhang + Show 12 more

Open Access

https://doi.org/10.1021/acsami.6b02544

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Abstract

Hybrid colloidal quantum dot (CQD) solar cells are fabricated from multilayer stacks of lead sulfide (PbS) CQD and single layer graphene (SG). The inclusion of graphene interlayers is shown to increase power conversion efficiency by 9.18%. It is shown that the inclusion of conductive graphene enhances charge extraction in devices. Photoluminescence shows that graphene quenches emission from the quantum dot suggesting spontaneous charge transfer to graphene. CQD photodetectors exhibit increased photoresponse and improved transport properties. We propose that the CQD/SG hybrid structure is a route to make CQD thin films with improved charge extraction, therefore resulting in improved solar cell efficiency.

Highlights

The hybrid solar cell is fabricated under ambient condition and graphene layers are inserted between colloidal quantum dot (CQD) layers via a layer-by-layer deposition method
One to two drops of single layer graphene (SG) solution was deposited onto the PbS surface and the substrate was subsequently washed with methanol and ethanol. 1,2-Ethanedithiol (EDT) solution (0.02 vol% in acetonitrile) was used for electron blocking/hole transport layer in a junction solar cell
The graphene layer inserted between CQD layers enables efficient extraction and transfer of photoinduced electron from QD to the adjacent graphene due to its high carrier mobility and lower energy level to the LUMO of PbS (Figure 1b)

Summary

INTRODUCTION

Colloidal quantum dots (CQDs) are known to have outstanding optical and electrical properties, which has led to extensive studies of generation optoelectronic devices such as light emitting diode, photodetectors, field effect transistors, and photovoltaics.[1−7] In particular, the CQD’s tunable bandgap has the potential to cover the entire solar spectrum and harness photon energies more efficiently compared to conventional solar cell.[8−10] To date, device efficiency improvements have been achieved by surface ligand engineering, substitution doping and/or multijunction device architectures.[11−15] To further improve the performance of CQD solar cells, the field has focused on the efficient extraction and transport of photogenerated charge carriers under incident light illumination through the fabrication of favorable energy band alignment of heterojunctions by surface functionalization[16−18] and/or the introduction of hybrid structures with CQD and nano carbon materials.[19−21] in spite of these rapid advances in device performance, the cell efficiency still lags behind other emerging solar cell technologies. We demonstrate a graphene/lead sulfide (PbS) CQD hybrid solar cell that shows enhanced photovoltaic performance dependent on the number of graphene injection layers. The hybrid solar cell is fabricated under ambient condition and graphene layers are inserted between CQD layers via a layer-by-layer deposition method. By employing various analytical techniques, graphene promoted exciton dissociation and improved charge transport in photoexcited PbS are hypothesized to be the origin of this efficiency enhancement

EXPERIMENTAL DETAILS

RESULTS AND DISCUSSION

CONCLUSION

■ ACKNOWLEDGMENTS

■ REFERENCES