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ZnO films developed via inkjet printing technology for application in dye sensitized solar cells (DSSC)

Nicholas Schulman1,2, Wolfgang Voit2 ,Valter Ström2, Lyuba Belova2

1Department of Chemical Engineering, The City College of New York, New York, NY, USA2Division of Engineering Material Physics, Department of Materials Science and Engineering, Royal Institute of Technology, Stockholm, Sweden

INTRODUCTIONEffects on the efficiency of the DSSCs via changing the parameters of the design

is the major focus of this study. Introduction of a blocking layer, which will

physically separate the nanostructured anode and the conducting layer of the

substrate, is a parameter of focus as well as the transparency of the blocking

layer. Another will be the thickness and structure of the nanostructured anode,

which will be created via inkjet printing of a liquid solution that will be

annealed to form a micro thin film with nano-porosity. The effects of the

parameters on the performance efficiency of the DSSC are studied via IV curves

created with a standardized lighting source. Structural characterization of the

fabricated thin films is done via Nova 600 SEM/FIB along with a Siemens

D5000 x-ray diffractometer.

BACKGROUND

ACKNOWLEDGEMENT • This work was partially supported by the IRES program through funding from the

National Science Foundation under Award NSF-OISE-1358179.

• Introductory lab training provided by Professor Ilona Kretzschmar under the mentorship of Paulina Librizzi.

EXPERIMENTAL DETAILS

REFERENCES• Basu, K. et al. Enhanced photovoltaic properties in dye sensitized solar cells by surface

treatment of SnO2photoanodes. Sci. Rep. 6, 23312; doi: 10.1038/srep23312 (2016).

• Chan, Dayna. "Development of an Inkjet Printing System on a Flatbed Router." (2010).

RESULTS

CONCLUSIONS/FUTURE WORK• Data acquired from initial testing of DSSCs is a starting point, but will need to be accompanied

by results in order to fully understand effects of varying individual parameters.

• More DSSCs will need to be constructed and tested to further determine which parameters with respect to the blocking layer and photoanode improve the efficiency of our cells.

• Investigation into the control of the microstructure of the ZnO films to understand how one can determine what factors effect the development of specific microstructures.

• Development of nanostructured photo anodes was completed via inkjet printing using the printhead shown in Figure 2.

• Precursor ZnO ink was made by combining zinc acetate dihydrate in a 1:1 molar ratio with ethanolamine in a solution of 2-isopropoxyethanol

• Printed films were deposited on a preheated substrate and further dried for removal of the organic solvent

• For building up thicker films with the inkjet printer each layer of precursor deposited was dried for a certain duration then another layer was deposited. This process was repeated until the desired thickness was reached.

• Films after printing and further drying were subsequently annealed in a tube furnace for period of time allowing complete removal of solvent and formation of nanocrystalline porous film.

• Post annealed films were characterized via microscopy tools (SEM/FIB) to determine qualities of microstructure and thickness of films

• Creation of ZnO films via inkjet printing was problematic with respect to control over microstructure and topography of thicker films as surface tension effects and agglomeration of film became more pronounced.

• SEM images of thick ZnO films (Figures 5 and 7) show effects of drying time per layer deposition and provide and region in which drying can be optimized from film development.

• Efficiency data from tested solar cell indicates reasonable results with respect to efficiency data from previous summer results with similar testing parameters.

SEM images from nanocrystalline films developed via inkjet printing and IV data from constructed DSSC with identical schematic to Figure 1.

DISCUSSION

Dye sensitized solar cells (DSSCs) are solar cells that utilize thin film

technology to construct a photosensitive anode and metallic cathode that work

in conjunction with an electrolyte to provide an electrical current. The DSSC

works on the photovoltaic effect, like all solar cells, but utilizes an

organic/metallic dye that acts as an electron carrier and releases charge

carriers upon photoexcitation. The anode, composed of a nanostructured (in

our case nano-porous) semiconducting material with high carrier mobility,

helps to provide a scaffold for the dye and a pathway so that charge carries,

upon release, can diffuse through the cell and create the current. The cathode is

simply another pathway created from a metallic element that guides the

electron back into the cell. The anode and cathode are physically separated via

the electrolyte and exchange charge carriers through the redox reaction

occurring with the electrolyte. Both electrodes are physically mounted onto a

substrate, with a thin layer of conducting material (𝑆𝑛𝑂2: 𝐹) between the

electrode and substrate.

Figure 1. Schematic of fully constructed DSSC with a nanostructured photoanode composed of 𝑇𝑖𝑂2. The DSSCs constructed in this study will have photoanodes composed of ZnO, a semiconducting material. The N719 is the metallic dye used to provide charge carriers and will be the same one used in this study.

Intensity (Wm-2) 1000

Eff (%) 0.151

Voc (V) 0.405

Jsc (mAcm-2) -1.251

FF 0.298

Area (cm2) 0.42

Figure 2. Schematic of an Xaar 126 printhead, which is the printhead used for developing thin films of ZnO via inkjet printing. The inkjet printing works on a drop on demand principle and uses a piezoelectric material as an actuator for releasing ink.

Figure 3. SEM image of ZnO film created with a precursor ink of .6M and annealed at 400°C for 1hr.

Figure 4. SEM image of cross section of ZnO film. The film was section with a focus ion beam. This film represents a single layer of ZnO when printed.

Figure 5. SEM image of ZnO film created by printing 5 layers with a drying temperature of 80°C and 10min of drying per layer.

Figure 6. SEM image of cross section of film from Figure 5. Extreme drying of the film has resulted in uneven thickness and surface topography of the film.

Figure 11. Data acquired from the graph in Figure 10. Efficiency of DSSC is within expected range, and data shows improvement of FF is needed.

Figure 9. SEM image of cross section of Figure 7. No drying between passes has improved surface topography but spreading of film has resulted in loss of thickness.

Figure 7. SEM image of ZnO film created by printing 10 layers with not drying between the printed layers.

Figure 10. IV curve generated from a DSSC tested under standardized conditions (1 Sun Illumination = 100mW/cm^2).