Characteristics of a New Copolymer For Bulk Heterojunction Solar Cells

<p>Organic solar cells have attractive aspects like flexibility, light-weight, environment-friendliness and low-cost due to manufacturing-ease on large area substrates using roll-to-roll processing, solution casting or screen printing. Most high performance organic solar cells utilize tandem structure with wide band gap polymer as a front cell material and low band gap polymer as a rear cell material. Since poly(3-hexylthiophene) (P3HT) has higher band gap ~1.9 eV and absorbs the higher energy photons, it is the most frequently used front cell material for tandem solar cells. However, the HOMO of P3HT is -5.0 eV, generating a Voc around 0.6 V. This limits the device performance of an organic solar cell. In this work, a new wide band gap copolymer poly{2-Octyldodecyloxy -benzo [1,2-b;3,4-b]dithiophene-alt-5,6-bis(dodecyloxy)-4,7-bis(dithiophen-2-yl)-benzo [c][1,2,5]-thiadiazole} (PBDT-ABT-2) synthesized by a post- doctoral student, Dr Qiliang Chen was studied and applied in an organic solar cell with a device structure of glass/ITO/PEDOT:PSS/PBDT-ABT-2:PCBM/Ca/Al. Donor/acceptor ratio, solution concentration and spin-speed for active layer deposition were optimized. PBDT-ABT-2 had lower HOMO energy level, as evidenced from cyclic voltammetry and higher Voc than P3HT, as evidenced from current density vs voltage characterization. The 1:1 donor/acceptor ratio with a solution concentration of polymer (10 mg) + PCBM (10 mg) in 1 mL of DCB had the highest device performance with a power conversion efficiency of 3%, short-circuit current of 7.63 mA/cm², open-circuit voltage of 0.71 V and a fillfactor of 53.74%. Since PBDT-ABT-2 has higher Voc and wider band gap, it can be used as front cell material in tandem device structures. Future work can include blending of copolymer PBDT-ABT-2 with acceptor materials having higher LUMO energy levels to increase V_oc. Optimization of processing conditions using additives, solvent annealing and thermal annealing to improve active layer morphology and current density.</p>

Name thesis:degree_name

Master of Science (MS)

Level thesis:degree_level

Thesis - University Access Only

Discipline thesis:degree_discipline

Electrical Engineering and Computer Science

Year dc:date.available

2013

Author dc:creator

• Maharjan, Purna P

Contributors dc:contributor

• Qiquan Qiao
• David Galipeau

• Electrical and Computer Engineering

Statement dc:rights

• Copyright 2013 Purna P. Maharjan

Language dc:language

en

Repository record dc:identifier

https://openprairie.sdstate.edu/etd/1575

OAI identifier oai:identifier

oai:openprairie.sdstate.edu:etd-2577