Photovoltaic Cells incorporating Organic and Inorganic Nanostructures

Transcription

1 Photovoltaic Cells incorporating rganic and Inorganic Nanostructures Jiangeng Xue Department of Materials Science and Engineering University of Florida, Gainesville, FL, USA NSF/NR PV Workshop Sept. 2-21, 212

2 History and status Recent development utline PV cells with organic nanostructures Polymer:colloidal nanocrystal hybrid PV cells ptical management Challenges and opportunities

3 Publications in Each Year Rapid Development of the PV Field Special issue on rganic Photovoltaics: Polymer Reviews, Vol. 5, No. 4 (21) % annual growth Updated (9/212) riginal (7/21) 1 1 Data from ISI Web of Science Year Topic=((organic or polymer) and (photovoltaic or solar cell)) J. Xue, Polym. Rev. 5, 411 (21).

4 Think about grass, trees, plants

5 Vertical Molecular Nanostructures Al BCP PCBM CuPc (donor) PCBM (acceptor) IT CuPc nanorods With stationary substrate With rotational substrate Molecular Flux Nanorod α 1 nm 1 nm ω Substrate blique Angle Deposition 1 nm 1 nm Y. Zheng et al., rganic Electronics (29); Polym. Rev. (29); IEEE J. Sel. Top. Quantum Electron. (21).

6 J (ma/cm 2 ) CuPc Nanorod/PCBM Films and Devices EQE (%) Spin-coating 1 nm Low PCBM loading High 1 nm PCBM loading 8 4 CuPc/PCBM bilayer CuPc NR/PCBM V (V) 1 Planar Planar-NR (nm) Y. Zheng et al., rganic Electronics (29); Polym. Rev. (29); IEEE J. Sel. Top. Quantum Electron. (21).

7 Absorbance J (ma/cm 2 ) Absorbance y (nm) PbPc 1 nm 2 nm 3 nm 4 nm Crystalline Molecular Template Monoclinic phase on bare IT Triclinic phase (a) (c) 5 nm PbPc on pentacene on Si (b) (d) (e) Profile x (μm) nm 2 nm 3 nm 4 nm w/ pentacene template PbPc thickness: (a) Å, (b) 2 Å, (c) 5 Å, (d) 1 Å, (e) 2 Å 5 None Pentacene CuPc ZnPc (nm) W. Zhao et al., rg. Electron. 13, 129 (211). V (V)

8 Hybrid rganic-inorganic PV Cells: Motivation Incorporation of inorganic semiconductors in polymer-based PV devices may improve charge transport and enhance environmental stability Inorganic semiconductor can also compliment the absorption of polymer Colloidal-synthesized semiconductor nanocrystals could be processed together with polymers in solutions W. U. Huynh, J. J. Dittmer, and A. P. Alivisatos, Science 295, 2425 (22).

9 Hybrid Polymer:CdSe Nanocrystal Systems for Photovoltaics Al =P =P CdSe =P =P Pyridine ligand exchange N S N S CdSe SN SN P3HT:CdSe PEDT:PSS IT Glass substrate TP: a spacer of 11Å 3.2 Ligand exchange for CdSe nanocrystals Dissolve in chlorobenzene and pyridine (9:1 in volume) mixed solvent Al 5.1 IT 5.2 PEDT: P3HT PSS CdSe

10 J (ma/cm 2 ) J (ma/cm 2 ) EQE (%) Effect of Nanosphere Size sun AM1.5G V (V) 4. nm 5. nm 6.1 nm 6.8 nm Larger size nanocrystals lead to higher J sc and η P, likely due to reduced defect density with fewer atoms on nanocrystal surface. J. Yang et al., Sol. Energy Mater. Sol. Cells 95, 476 (211) nm 4. nm Wavelength (nm) 1 3 Electron-only devices: Al/P3HT:CdSe/Al nm, e ~1-4 cm 2 /V s 4. nm, e ~1-5 cm 2 /V s V (V)

11 P3HT/CdSe Film: Importance of Morphology Show somewhat percolating structures of CdSe nanospheres, allowing for good transport of photogenerated electrons. J. Yang et al., Sol. Energy Mater. Sol. Cells 95, 476 (211).

12 Current density (ma/cm 2 ) EQE (%) (2) (21) (12) (11) Intensity (a.u.) (13) (112) (1) (2) (11) Hybrid PV Cells with a Zn Nanosphere Layer Al Zn NPs P3HT:CdSe photoactive layer PEDT:PSS IT Glass substrate 4 2 P3HT:CdSe P3HT:CdSe/Zn 5 4 Zn NPs Bulk Zn (degree) P3HT:CdSe P3HT:CdSe/Zn Zn NPs size ~3 nm Nano Today 5, 384 (21); Nat. Photon. 5, 543 (211) Voltage (V) P :.8% 1.5% (5. nm) 1.6% 2.5% (6.5 nm) Wavelength (nm) L. Qian et al., J. Mater. Chem. 21, 3814 (211); J. Yang et al., J. Appl. Phys. 111, (212).

13 Wavelength (nm) IT PEDT:PSS P3HT:CdSe Zn Al Wavelength (nm) IT PEDT:PSS P3HT:CdSe Al Efficiency Enhancement with Zn NPs Combination of electronic, optical, and structural effects! Blocking hole leakage to cathode 4 Preventing exciton quenching by cathode Transparent optical spacer for enhanced light absorption 5 Reducing damage to active layer during cathode deposition (less defects formation 6 in active layer) Al 5.1 IT 5.2 PEDT: P3HT Zn PSS CdSe

14 Current density (ma/cm 2 ) PCE (%) Effect of Zn Layer on Device Aging 4 P3HT:CdSe/Zn NPs After 7 days Fresh Without Zn Thicker Zn Thinner Zn Voltage (V) Times (day) Without the Zn layer, the devices have shelf lifetimes of a few hours; but with the Zn layer, the device retain >6% of the initial efficiency after 7 days (stored in air)

15 Current density (ma/cm 2 ) EQE Hybrid PCPDTBT:CdSe NP/Zn NP cells w/o Zn w/ Zn w/ Zn, 6 days.5 w/ Zn w/o Zn Voltage (V) Wavelength (nm) PCPDTBT (E g = 1.5 ev) η P = 3.5% in device with Zn NPs under 1 sun AM1.5G illumination, compared with 2.3% without Zn. For the device with the Zn NP layer, 3% loss in η P after 6 days of exposure to air without encapsulation R. Zhou et al., Nanoscale 4, 357 (212).

16 J SC /P (A/W) Hybrid Solar Cells: Effect of EDT Treatment Device Al Polymer:CdSe NCs PEDT:PSS IT Glass Jsc (ma/cm 2 ) HS CdSe Voc (V) 2 nm SH FF η p (%) P3HT, w/o EDT P3HT, w/ EDT PCPDTBT, w/o EDT PCPDTBT, w/ EDT R. Zhou et al., submitted. Current density (ma/cm 2 ) P (%) PCPDTBT:CdSe nanorods w/o EDT w/ EDT Voltage (V) PCPDTBT:CdSe w/ EDT w/o EDT 1 1 P (mw/cm 2 )

17 Hybrid Solar Cells: Effect of EDT Treatment Intensity (a.u.) Transmittance (a.u.) L-type (neutral) ligands e.g. TP P P H P P P P H H P P CdSe P P PA H Cd 2+ P P TP -C-H EDT treated Pyridine-exchanged Purified -P= Wavenumber (cm -1 ) X-type (charged) ligands, phosphonic acid (PA) Purified Ligand-exchanged EDT treated, w/o annealing EDT treated, w/ annealing P 2p Binding energy (ev)

18 Grafting Reative ligomers on Nanocrystals Anchoring functional group e - PE-acid (E g = 2.9 ev) ligomer or polymer backbone Inorganic nanorod h + T7-acid (E g = 2.5 ev) BTD-acid (E g = 1.8 ev) With John Reynolds, Kirk Schanze, Paul Holloway Jiangeng Xue

19 Nanocrystal:Grafted ligomers ester (non-reactive) acid (reactive) ester form acid form R. Stalder et al., Chem. Mater. 24, (212).

20 Light Trapping with Pyramidal Rear Reflector Improvement of Jsc (%) Flat Pyramidal Total internal reflection 6 4 Exp. Calculation Ideal (no absorption loss) Thickness of Active Layer (nm) SEM image of Pyramids W. Cao et al., Appl. Phys. Lett. 99, 2336 (211)

21 Polymer Microlens Array by Soft Lithography PS microspheres Norland optical adhesive 3 Si wafer PS = 1μm S.-H. Eom et al., rg. Electron. 12, 472 (211); E. Wrzesniewski et al., Small 8, 2647 (212). Jiangeng Xue

22 J (ma/cm 2 ) PV Cells with Microlens Array Enhancement (%) 6 4 SubPc/C 6 (12/y nm) J sc P Simulation C 6 thickness, y (nm) SubPc/C 6 (12/4 nm) -2-4 w/o MLA -6 w/ MLA V (V) Architecture η p (%) % w/o MLA w/ MLA incr. P3HT:PCBM P3HT:PCBM/Zn PCPDTBT:CdSe/Zn PCPDTBT:CdSe PBnDT-DTffBT:PCBM* J. D. Myers et al., Energy Environ. Sci. 5, 69 (212). * Polymer from Wei You (UNC)

23 Challenges and pportunities Control of molecular/polymer assembly Desired nanostructures or other hierarchical structures Molecular orientation and crystal structures Robust bulk heterojunction structure insensitive to molecular structure modification and processing condition variation rganic-inorganic hybrid material interface: morphological, chemical, and electronic properties Nanocrystal surface passivation Nanorod alignment Energy level alignment Development of Cd-free nanocrystals 2 nm Near IR absorbing materials (organic & inorganic) Aligned ptical management Appropriate light trapping structure Large area manufacturability As-coated 5 nm

24 Acknowledgments Students and postdocs in my group at University of Florida: Dr. Jihua Yang Dr. Ying Zheng Dr. Wei Zhao Bill Hammond Sang-Hyun Eom Jason D. Myers John Mudrick Robel Bekele Shuang Zhao Yixing Yang Weiran Cao Renjia Zhou Ed Wrzesniewski Jiaomin uyang Vincent Cassidy $$ from NSF CAREER and DE SETP