B Team - Molecular Photonics

Key Publications

  • Timalsina, A.; Hartnett, P. E.; Melkonyan, F. S.; Strzalka, J.; Reddy, V. S.; Facchetti, A.; Wasielewski, M. R.; Marks, T. J., New donor polymer with tetrafluorinated blocks for enhanced performance in perylenediimide-based solar cells. J. Mater. Chem. A 2017, 5 (11), 5351-5361.

  • Zhou, N.; Dudnik, A. S.; Li, T. I. N. G.; Manley, E. F.; Aldrich, T. J.; Guo, P.; Liao, H.-C.; Chen, Z.; Chen, L. X.; Chang, R. P. H.; Facchetti, A.; Olvera de la Cruz, M.; Marks, T. J., All-Polymer Solar Cell Performance Optimized via Systematic Molecular Weight Tuning of Both Donor and Acceptor Polymers. J. Am. Chem. Soc. 2016, 138 (4), 1240-1251.

  • Melkonyan, F. S.; Zhao, W.; Drees, M.; Eastham, N. D.; Leonardi, M. J.; Butler, M. R.; Chen, Z. H.; Yu, X. G.; Chang, R. P. H.; Ratner, M. A.; Facchetti, A. F.; Marks, T. J., Bithiophenesulfonamide Building Block for pi-Conjugated Donor-Acceptor Semiconductors. J. Am. Chem. Soc. 2016, 138 (22), 6944-6947.

  • Dudnik, A. S.; Aldrich, T. J.; Eastham, N. D.; Chang, R. P. H.; Facchetti, A.; Marks, T. J., Tin-Free Direct C–H Arylation Polymerization for High Photovoltaic Efficiency Conjugated Copolymers. J. Am. Chem. Soc. 2016, 138 (48), 15699-15709.

  • Hartnett, P. E.; Timalsina, A.; Matte, H. S. S. R.; Zhou, N.; Guo, X.; Zhao, W.; Facchetti, A.; Chang, R. P. H.; Hersam, M. C.; Wasielewski, M. R.; Marks, T. J., Slip-Stacked Perylenediimides as an Alternative Strategy for High Efficiency Nonfullerene Acceptors in Organic Photovoltaics. J. Am. Chem. Soc. 2014, 136 (46), 16345-16356.

  • Guo, X. G.; Zhou, N. J.; Lou, S. J.; Smith, J.; Tice, D. B.; Hennek, J. W.; Ortiz, R. P.; Navarrete, J. T. L.; Li, S. Y.; Strzalka, J.; Chen, L. X.; Chang, R. P. H.; Facchetti, A.; Marks, T. J., Polymer solar cells with enhanced fill factors. Nat Photonics 2013, 7 (10), 825-833.

Novel Active Layer Materials

Also important in studying and improving the efficiency of organic photovoltaics is the development and incorporation of novel active layer materials. The Marks group, in collaborations with other groups, has successfully incorporated a new small molecule squaraine derivative [1] as the donor material with a fullerene acceptor, with power conversion efficiencies of η = 1.2%. The B Team also collaborates with the D Team in studying the new materials, both n- and p-type, that D Team members develop for organic field effect transistors that show promising characteristics for organic photovoltaics. In addition, B Team members are involved in the design and synthesis of new small molecule acceptors for organic photovoltaics to replace the current industry standard fullerene.

Scheme 1. Synthetic Route to Squaraine Donors (i) DMF, t-BuOK, RBr, 25°. (ii) N,N-Diphenylhydrazine hydrochloride, EtOH, 4 h reflux. (iii) Squaric acid, azeotropic mixture, reflux.


Figure 1
. (A) J−V response of 1:PCBM BHJ OPV devices as a function of D:A ratio; 1:1 ratio from ODCB (140 nm, black line), 1:1 ratio from ODCB (30 nm, red line), 1:3 ratio from CHCl 3 (140 nm, pink line), and 1:3 ratio from CHCl 3 (30 nm, blue line). (B) Dark current measurements for 1:1 ratio films from ODCB (30 nm, red line), 1:3 ratio from CHCl 3 (140 nm, pink line), and 1:3 ratio from CHCl 3 (30 nm, blue line)

Electron Blocking Layers in BHJ Solar Cells

The electron donor (hole transporter) and electron acceptor (electron transporter) are intermixed in bulk heterojuction cells. Such intermixing is extremely important for optimal charge separation but it unfortunately provides opportunities for the charges to go to the wrong electrodes because both the electron and the hole transporters are in physical contact with both the electrodes. In order to prevent the electrons from going to anode, we add an interfacial layer between the anode and the active material. Because of the function it serves in the cells, we call it the electron blocking layer (EBL).

The Mark’s Group has designed some really interesting EBL materials in the past couple of years. TPDSi 2 is a molecule that was first developed in the Marks Group as an EBL in OLEDS but it also worked really well as an EBL in MDMO-PPV cells. The energy level of a TPDSi 2-TFB composite layer makes is a good EBL for such cells.

Another EBL that we have designed is the inorganic Nickel Oxide (NiO) layer. The energetics of NiO and donor polymer P3HT match well.The EBL we have designed affords higher efficiencies and better lifetimes over the industry standard PEDOT:PSS as EBL.

Organic photovoltaic (OPV) modeling

We develop device models, defining and quantifying loss mechanisms in OPVs. If an OPV cell performs at 5% efficiency, what exactly is happening to the other 95%? We are currently studying key loss mechanisms (e.g., exciton dissociation, charge recombination), developing more specific models of these processes, and determining how changes to particular materials parameters (e.g., conductivity, dielectric constant, etc.) can enhance these processes and, ultimately, overall OPV power conversion efficiency.

Figure 2.
Evaluation of the effects anode conductivity and cell size have on power conversion efficiency. Note that the zero loss case (upper left hand corner of graph) has a power conversion efficiency of 13.6%

Recent Publications

Recent Journal Covers

Inorganic Chemistry, October 7, 2002
Chemistry of Materials, January 10, 2006

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