SELECTIVE METHODS IN FULLERENES CHEMISTRY

Sara Vidal Estremera Molecular Materials Group, UCM

Supervisors: Prof. Nazario Martín

Dr. Salvatore Filippone

Introduction

Great development of renewable energies

Solar energy is the cleanest and most abundant

bicontinuos polymer-fullerene composites

Organic solar cell • Lightweight • Cheap • Flexible

Bulk heterojunction (BHJ)

Background

• High electron affinity

• Ability to transport charge

• Low reorganization energy

300 350 400 450 500 550 600 650 7000,0

0,5

1,0

1,5

2,0

2,5

3,0

C60

C70

Ab

sorp

tio

n

Wavelength (nm)

C70 suitable candidate for

more efficient PV devices

C70

C60

UV-vis

Background

Maroto, E. E.; de Cózar, A.; Filippone, S.; A. Martín-Domenech, Suárez, M.; Cossío, F. P.; Martín, N.

Angew. Chem. Int. Ed., 2011, 50, 6060-6064.

• Loss of spherical symmetry of C60

• Four types of double bonds

Background

Fullerenes in photovoltaic devices

Bulk heterojunction solar cells Photovoltaic process

Hole transport

Electron transport

Anode Cathode

Photon

h+ e- 1. Photon absorption

2. Exciton formation

3. Charge transfer

4. Charge transport

Campo eléctrico Electric field Control on the morphology donor/aceptor mixture better efficiencies

Electric field

Objective

Campo eléctrico

α-[70]DPM α-[70]PCBM

Design of new compounds, [70]DPM and [70]PCBM, with a high isomeric purity able to improve the degree of

crystallization in the active layer

Results

Applications in photovoltaic devices: new

methodology for synthesis of DPMs

Classic Method

Results

Selective method based on mild conditions

Applications in photovoltaic devices: new

methodology for synthesis of DPMs Photochemical Method

Results

Thermal method

a-siteisomer + b-siteisomer

Photochemical method

a-siteisomer

Mild conditions: Not high temperatures Not strong bases

1H-NMR (300 MHz, 298K, CDCl3)

+

a b

R= C4H9

Results

HPLC profile photochemical method

Tol/MeCN 9:1; 1ml/min, 25ºC

Results

Applications in photovoltaic devices: new

methodology for synthesis of PCBM

Classic Method

3:1

The result is a mixture of three regioisomers

Results

Applications in photovoltaic devices: new

methodology for synthesis of PCBM

Photochemical Method

Photochemical irradiation leads to the predominant formation of a single siteisomer

Results

74 %

26 %

HPLC profile PCBM thermal method

Tol/MeCN 1:1; 1ml/min, 25ºC

96 %

4 %

HPLC profile PCBM photochemical method

Tol/MeCN 1:1; 1ml/min, 25ºC

Results

Electrochemical properties

[70]DPM fotoquímico [70]PCBM fotoquímico

CV en o-DCB:MeCN 4:1 a 100 mVs-1; electrolito soporte, n-Bu4NPF6 (0.1M)

Compuesto E1red E2

red E3red E4

red

C70 -0.99 -1.39 -1.81 -2.20

[70]PCBM -1.11 -1.49 -1.88 -2.29

[70]DPM4 -1.10 -1.48 -1.88 -2.29

Summary

We present a new methodology to obtain methanofullerene

derivatives, [70]PCBM and [70]DPM, based on mild and selective conditions, that leads to the predominant formation of a single siteisomer.

[70]Fullerene derivatives as acceptors present a higher photovoltaic efficiency.

Isomeric purity allows greater control on the nano-morphology of donor/acceptor mixture (polymer/fullerene) which results in a better photovoltaic response.

Acknowledgments

Supervisors: Prof. Nazario Martín Dr. Salvatore Filippone

Molecular Materials Group