Dye-sensitized Solar Cells: Options, Problems, and Inspirations for Water Treatment

Transcription

1 Dye-sensitized Solar Cells: Options, Problems, and Inspirations for Water Treatment F. Marlow El Gouna, Febr Fischer-Tropsch Ziegler-Natter Coffein extract. Now: Catalysis Porous materials MPI für Kohlenforschung Mülheim an der Ruhr Outline Options Problems I: Practical realization Problems II: Understanding Inspirations for water treatment Operation principle V Fig. from Carp et al. worka - + 1

2 The solar cell research field Options Up to 12% < 10 $/m² Environme ntalfriendly FhG-ISE Wikipedia Simple fabrication Smallscale fabrication possible No technology barrier No financial barrier Low weight Tandems possible Decorative 2

3 Problems I: Practical realization Top values difficult to realize (often 6%) Fluctuations in efficiency (in a cell, cell-to-cell) Fluctuations in lifetime Size dependence Electrolyte dependence (3 ions, additives, solvent) Most works use glass supports Hinsch 2012 (Fraunhofer ISE): 12% on < 1 cm² (EPEL, 2011) 11% on 1 cm² (Sharp) 8 % on 18 cm² (Sony) 5 % on 100 cm² (FhG-ISE 2012) All these have influence on applications! Our DSSC projects Improved DSSC anodes Reliable fabrication (reproducibility, stability) Changed composition -> E CB -> V oc Time-resolved characterization - J(t) Improved theoretical understanding Photon management (A. Khalil, S. Abdellatif) I - 3

4 Problems II: Understanding Current research work: Is the Charge Transport in Dye-sensitized Solar Cells really understood? F. Marlow, A. Hullermann, L. Messmer, Adv. Mater. (2015) in press. Charge transport Measurement of transients Barnes/J/Grätzel/ O Regan 2013 Review 42 pages ca.100 physical parameters 144 references Electrical response behavior - + Sens I 3- I - + 2e - FTO A V Response after a laser pulse Current theoretical background: The standard model Three basic assumptions: (1)The transient effects can be ascribed to field-free electron diffusion. (2)The signal is associated with the photo-e - reaching the outer contacts. (3)The diffusion is heavily modified by the interaction with e - trap states. Model Parameters + Interpretations J?? t Barnes, Miettunen, Li, Anderson, Bessho, Grätzel, O'Regan, Adv. Mater. 2013, 25,

5 Experimental details Standard (?) Laser: 8 ns Effective detection resolution: 1 µs Blind time: 4 µs Test with Si-SC: Reaction time below 20 µs DSSC electrolyte: based on ethylene glycol Laser unit: Flash lamps + power supply Figure from A. Hullermann, MSc-Thesis Results: The J-transients F1 F2 5

6 Dependence on external parameters A closer look at the voltage dependence J Steady-state electrons Pulse electrons Basics: JV curves J J sc F3 V oc V 6

7 Dependence on internal parameters F4 Discussion Internal interface voltage: U ii = U P + J 0 R S+ Model: Φ 1 = k 1 N nss Φ 2 = k 2 N nss Φ 3 = k 3 (N nss ) 2 N CB = αln(1+β N hν ) N hν -number of absorbed photons 7

8 Conclusions from J-transients F1-F4: Contradictions to the current interpretation. F1: Delay (1) J field-free electron diffusion F2: t rise (2)J e - at outer contacts F3: U-effects (3)J trap states F4: No Einstein relation: t char 1/D (d char ) 2 No easy repair possibility Direct field effects on charge transport (likely) Nonlinear recombination channel (likely) There is diffusion. But: What exactly is diffusing? => Open: Determination of D More rational design? What is really happened after laser excitation? Primary charge separation Formation of an internally charged BHJ De-charging of the ic-bhj fs J ps No current response ns J µs (?) Regeneration No current response µs J ms Simultaneous escape of both charges only Measurable current I - 8

9 Inspirations Not very successful Solar energy TiO 2 for electricity Photochemistry - environmental (Air, water!!) -synthesis A e - e - A High quantum efficiency I - TiO 2 Low quantum efficiency h + h + B B (3 problems!) DSSC-inspired hypothetical solution A e - e - e - A B h + B C C Interesting example: B = OH - B = HO C = hydrocarbons C = J 9

10 Project outline Idea: new type of photocatalyst 2 years Proof of principle 1 year Adaptation to a emulsion or droplet system Image of a macroscopic droplet system (J. Akilavasan et al.). Application example Summary Options 12 % without high-tech + J Problems I: Practical realization Problems II: Understanding Need for a new model Open measurement problem for D New rational design possible? Inspirations for water treatment Cooperation? 10

11 Thanks Abigail Hullermann Lisanne Messmer Parvin Sharifi J. Akilasavan, R. Goddard, D. Kasper, G. Mane, M. Mischner, D. Naumann, E. Samsonova, F. Schüth, D. Rainko, S. Wall A. Khalil RESOLV RUHR EXPLORES SOLVATION CLUSTER OF EXCELLENCE - EXC 1069 IMPRS-SurMat NanoScape Thank You! 11