( P ) Thales Photo-Electrochemical Techniques. Outline. Photo-Electrochemical Set-Up. Standard Solar Cell Measurements

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1 Outline Thales hoto-electrochemical Techniques Dynamic- and Spectral Methods for Measurements on DSSC, OSC, OLED and Electro-Chromic Devices C.-A. Schiller Standard Solar Cell Measurements Basics and the Applications of CMS/CMVS Additional dynamic techniques for Solar Cells Spectral resolved hotocurrent determination Optical Absorption / Extinction measurement in an electrochemical set-up Dynamic Transmittance / Reflectance measurement hoto-electrochemical Set-p Zennium Electrochemical orkstation Standard Solar Cell Measurements LED light source carrier with photosense amplifier and lluminator Cell under test Light source control potentiostat. (feedback control photosensor hidden behind the cell) Maximum Voltage, Current, ower, Fill Factor and CE of an OSC under blue illumination at /m². Force-response couples for ES, MVS and MS The Three Facts of a Solar Cell: Voltage Current-ntensity No information about the photoelectric process through ES Two additional force-response couples can be used for further transfer function analysis: Dynamic hotocurrent vs. ntensity MS Dynamic hotovoltage vs. ntensity MVS = a ( ) = a ( ) = a ( ) = Voltage across, = Current through the object. = llumination ntensity Anode p + n n + V A Cathode h ν cell current cell voltage Each transfer function emphasizes different parts of the system! ES MS MVS Z ( ω) =, [ ] = Ω Z ( ω) =, [ ] ( ω) =, [ ] A m = V m =

2 The Aim of MS / MVS when optimizing SC Comparison Between Conventional MS and CMS The competition between photo-charge recombination and charge diffusion affects the efficiency of OSC & DSSC. R i = MS R i = SC C SC ( ω) =, ( ) = ω, MS MVS = A m V m = Dynamic photocurrent vs. intensity MS: electron diffusion time constant τ c dominates at short-circuit under illumination. Dynamic photo-voltage vs. intensity MVS: electron recombination time constant τ r dominates at OC under illumination. The ratio - τ c / τ r determines the efficiency. Dynamic network analysis: join ES, MS & MVS results to find a common model. 7 Cell current ( ω) = LED current Cell voltage ( ω) = LED current Conventional MS: The LED control current is used as force signal information. The actual intensity and modulation is uncertain. Cell current Cell voltage ( ω ) = ( ) ω = ntensity ntensity CMS: The measured intensity is used as force signal information.the actual intensity is controlled with a photo-sensor at the site of the cell and regulated by means of an operational amplifier feedback circuit. MS & MVS on a ZnO-Based DSSC Analysis of the ZnO-Based DSSC MS & MVS Dynamic efficiency spectra measured on a ZnO based DSSC in Bode representation, on the left MS, on the right MVS Analysis of the dynamic efficiency spectra of a ZnO based DSSC in Nyquist representation. The circles indicate the measurement samples, the solid line curves the simulated spectra, modeling the electron diffusion and recombination time constants τ c and τ r,. On the left the MS with the breakpoint frequency /πτ c is depicted, on the right the MVS with /πτ r rinciple of a bulk hetero-junction type OSC OSC (Cr ( Cr-Al Al-Cr Cr-T T-CBM CBM-EDOT:SS EDOT:SS-Au) CMS / CMVS at Short Circuit Conditions photocurrent / µa - m phase / o photovoltage / V - m phase / o Donor Acceptor 7 7 Acceptor: CBM TO.7eV LMO.eV LMO.7eV Al.eV 7w w w m m m 7w w w Donor: T EDOT.eV OMO.eV OMO.eV K K K K K K m m K K K K

3 OSC mpedance Characteristics under Light Selected Dynamic Measurements on the OSC impedance / Ω phase / o impedance / Ω K 7 K K phase / o 7 Multiple Function Gradient calculation Complex Nonlinear Least Squares Fit ZCV arameter variation Measured spectra: Model Z: impedance C: photo-current ZCV(t,ω, n ) V: photo-voltage Deviations Z ( ω i ) Σ ( Z(ω i ) - ZCV(,ω i ) ) skalar deviation sum fit loop 7 7w_ocv w_ocv w_ocv K 7w w w C ( ω j ) Σ ( C(ω j ) - ZCV(,ω j ) ) V ( ω k ) Σ ( V(ω k ) - ZCV(,ω k ) ) Σ K K K K K at open circuit conditions K K K K K at short circuit conditions on the left: experimental results from ES, MS and MVS of the OSC. On the right: scheme of the Thales SM TRFT CNLS joined fitting procedure for three different kinds of spectral transfer functions: impedance, dynamic photocurrent and dynamic photo-voltage. Fit Results of the Dynamic Measurements on the OSC 7 Charge Extraction after N.. Duffy, L.M. eter et al N ser # hoto-active layer: hotocurrent source, breakpoint frequencies blocked hole diffusion in the porous layer electrostatic capacity olymer anode: finite length diffusion of holes in the anode layer electrostatic capacity Shunt loss shunt resistance Series loss 7 contact resistance. µa. Mz. Mz 7. KΩ s -/ 7.7 Ks -. nf. KΩ s -/. Ks -. nf. KΩ 7. Ω Assignment of the bulk hetero-junction OSC phases and processes to a dynamic equivalent circuit model Charge Extraction of a DSSC with different delay times between turning light off and start of discharging. The aim is the photo electron density distribution vs. potential hotocurrent Spectra: ncident hoton to Current Conversion Efficiency CE Typical CE of Alternative Solar Cells with Different orking rinciple Setup for CE measurements consisting of the Tunable Light Source with supply potentiostat and sample cell controlled by the Zahner Zennium 7 hotocurrent and CE measurements of two different DSSC and an OSC recorded with the Zahner tunable light source TLS

4 hoto-electrochemical Transmission / Absorption Measurements OSC and OLED orkfunction Vacuum Level TO p BG n Al TO p BG n Ca:Mg Setup for photo-electrochemical absorption/transmission measurements Band schemes of a typical OSC (bulk hetero-junction type, left) and an OLED (three layer type, right). p: hole transport layer (e.g. EDOT:SS), n: electron transport layer (e.g. left: CBM as - acceptor. right: Alq [tris(-hydroxyquinoline) aluminum]), BG: active band-gap material for photon absorption (left, e.g. T as -donor) respectively electron-hole recombination under light emission (right, e.g. r(ppy) = fac tris(-phenylpyridine) iridium). Extinction Spectra Series vs. Cell Voltage Referenced to Ag/AgCl AgCl. T-EDOT:SS EDOT:SS Film in Acetonitrile / TBA-F, under N., Absorption- and mpedance Spectra of an OSC / OLED olymer anion incorporation -.V +.7V hν hν -. V. +. V +. V extinction. +.7 V.. 7 wavelength / nm Extinction spectra series vs. cell voltage referenced to Ag/AgCl m-nacl of a T-EDOT:SS film in Acetonitrile / TBA-F (on the left) and the corresponding impedance spectra (on the right). Stability and Reversibility of the Film under Test Model Fit of the mpedance Spectra Series vs. Cell Voltage. extinction V at start -. V at end current / µa cycles mv/s +. mc -. mc impedance / Ω K K K +.7V +.V -.V phase / o 7 +.V +.7V -.V - m K K K K m K K K K. 7 wavelength / nm - potential / mv mpedance modulus (left) and phase angle diagram (right). Symbols: Experimental samples. Solid lines: Model Fit.

5 impedance'' / KΩ Model Fit of the mpedance Spectra Series. V 7 impedance' / KΩ -.V -.V ACN-TBA F Modeling & fit of the reduced state spectra (left) and the model used (right).,: inert hole transport layer with, porous distribution.,: active layer redox Faraday impedance, film assigned diffusion, 7 layer capacity with, porous distribution. T : electrolyte resistance. EDOT:SS TO 7 impedance'' / Ω Model Fit of the mpedance Spectra Series. +.V - +.7V ACN-TBA F +.7V - T - (oxidized) - EDOT:SS TO impedance' / Ω Modeling & fit of the oxidized states (left) and the model used (right).,: (slightly oxidized) hole transport layer with, porous distribution.,: (almost) fully oxidized active layer. : electrolyte resistance. ES, MS & MVS Joint Model Fit of the Reduced State. modulus phase / o K impedance / Ω m voltage eff. / V m - µ ACN-TBA F T 7 EDOT:SS TO Set-p for Dynamic Transmission / Reflection Measurements µ current eff. / A m - n m m K m m K TRFT-Modeling (solid lines) of the data (symbols) and the model used (inlay right).,: inert hole transport layer with, porous distribution.,: active layer redox Faraday impedance, film assigned diffusion, 7 layer capacity, photocurrent source with, porous distribution. 7 : electrolyte resistance. Setup consisting of a selective Light Source with supply potentiostat, the sample cell controlled by an additional slave potentiostat and the transmitted light sensor controlled by the Zennium main potententiostat Experimental Spectra ˆ + TR TR TR ˆ pot = = =, V ˆ e ˆ [ ] = pot ˆ + TR TR e TR ˆ gal = = = e, A ˆ e ˆ [ gal ] = pot gal c cˆ const = = ˆ e + c cˆ const = = ˆ + cˆ = e ˆ cˆ = e ˆ spectra of a the multilayer polymer film electrode TO - EDOT:SS - T in Acetonitrile / TBA-F at different wave lengths of nm (red curves) and 7 nm (blue curves)