Solution processed reduced graphene oxide/metal oxide hybrid electron transport layers for highly efficient polymer solar cells

Abstract

The solution to the all polymer solar cell that breaks the 10% efficiency barrier keeps getting closer, with ever more scrutiny on each component in the active device for better performance. Much effort has been expended on the hole transport layers and photo-active polymer blends in these solution deposited photovoltaic cells. In this study we examine the merits of incorporating solution deposited metal oxide and hybrid metal oxide/reduced graphene oxide (RGO) based electron transport layers (ETL) with a view to providing further improvements to the PV cell architecture. Low bandgap active layer blends of [3,4-b]thiophene/benzodithiophene (PTB7) and [6,6]-phenyl C70 butyric acid methyl fullerene (PC 70 BM) with efficiencies in excess of 7% are fabricated and the performance of four different ETL material systems based on TiO 2 , ZnO, TiO 2 /RGO, ZnO/RGO are compared to thermally evaporated optimised reference bathocuproine (BCP) PV devices. Hybrid metal oxide/RGO ETL incorporated solution processed devices show an improved device performance compared to metal oxide only devices, with the performance comparable to the thermally evaporated BCP with fill factors of 68% and short circuit currents reaching 15 mA/cm 2 . The enhanced performance of the RGO incorporated hybrid ETL points the way for novel transport layers for all solution processed devices. BodyGrowing concerns with regards to the diminishing supply of fossil fuels and the impact of such non-renewables on global warming has made solar energy generation an important area of research. Of the many types of solar-energy converting systems, organic photovoltaics have attracted significant interest due to their low cost, light weight and the printable nature on flexible substrates.

Effects of Mechanical Stretching on the Properties of Conjugated Polymers: Case Study for MEH‐PPV and P3HT Oligomers

“…Aiming to facilitate such analysis, Figure illustrates the alignment of the frontier levels of the evaluated polymers in relation to the HOMO and LUMO of typical acceptor compounds, as well as the work functions of electrodes commonly employed (or at least proposed) in flexible devices . In order to allow direct comparisons, our theoretical results for the HOMO values of the free MEH‐PPV and P3HT models were shifted to match the experimental HOMO values typically found in polymeric solutions of MEH‐PPV and P3HT …”

“…Alignments between the frontier energy levels of the polymers and the frontier levels/work functions of typical acceptors and electrodes employed in flexible organic devices . [Color figure can be viewed at wieyonlinelibrary.com] …”

PEIE capped ZnO as cathode buffer layer with enhanced charge transfer ability for high efficiency polymer solar cells

“…Oxygen can be easily adsorbed onto ZnO and form defects there [20,21], increasing the charge recombination and retarding the charge transfer at the interface (the second and third schematic drawings). However, by covering ZnO with ultrathin PEIE film, while the additional charge transfer pathways provided by ZnO [28] are reserved ( Fig. 4e and j), the defects on ZnO are greatly reduced by occupying ZnO by PEIE to reduce adsorbed oxygen (fourth schematic drawing).…”

“…Using reduced graphene oxide (RGO) modified ZnO as the CBL can also improve the PCE of device [27], which was attributed to the higher electron conductivity of RGO/ZnO nanocomposites than intrinsic ZnO as well as by reduction of interfacial resistance due to the RGO composite. Several thermal annealingfree PSCs have been reported recently [28][29][30][31]. For example, Cheng et al [29] improved the PCE of inverted polymer solar cells without thermal annealing by using ZnO NPs/Cs 2 CO 3 bilayer as CBL.…”

Interfacial Layer Engineering for Performance Enhancement in Polymer Solar Cells

“…Furthermore, the GO-Li containing cells exhibited enhanced stability versus the cells without the interlayer, which was attributed to the shielding effects of GO-Li against humidity. Silva and coworkers reported solution processed reduced GO and metal oxide (ZnO and TiO2) hybrid as cathode IFL for high-performance PSCs [99]. The device performance of the PSCs incorporating the nanohybrid IFL was comparable to that of cells using thermal evaporated bathocuproine (BCP) cathode IFL.…”