TY - JOUR
T1 - 2,7-Carbazole and thieno[3,4-c]pyrrole-4,6-dione based copolymers with deep highest occupied molecular orbital for photovoltaic cells
AU - Uddin, Mohammad Afsar
AU - Kim, Taehyo
AU - Yum, Seungjib
AU - Choi, Hyosung
AU - Hwang, Sungu
AU - Kim, Jin Young
AU - Woo, Han Young
N1 - Funding Information:
Uddin, Kim and Yum contributed equally to this work. This work was supported by the National Research Foundation (NRF) of Korea ( 2009-0093020 , 2012R1A1A2005855 ) and the New & Renewable Energy Core Technology Program of the Korea Institute of Energy Technology Evaluation and Planning (KETEP), granted financial resource from the Ministry of Trade, Industry & Energy, Republic of Korea (No. 20113010010030 , 20133030011330 ).
Publisher Copyright:
© 2015 Elsevier B.V. All rights reserved.
PY - 2015/5
Y1 - 2015/5
N2 - Three kinds of donor-acceptor (D-A) type photovoltaic polymers were synthesized based on 2,7-carbazole and thieno[3,4-c]pyrrole-4,6-dione (TPD). The conjugation of weakly electron (e)-donating 2,7-carbazole and strongly e-accepting TPD moieties yielded a deep highest occupied molecular orbital (HOMO) and its energy level was fine-controlled to be -5.72, -5.67 and -5.57 eV through the incorporation of thiophene (T), thieno[3,2-b]thiophene (TT) and bithiophene (BT) as a π-bridge. Polymer:[6,6]-phenyl-C71 butyric acid methyl ester (PC71BM) based bulk heterojunction solar cells exhibited a high open-circuit voltage (VOC) in the range, 0.86-0.94 V, suggesting good agreement with the measured HOMO levels. Despite the high VOC, the thiophene (or thienothiophene)-containing PCTTPD (or PCTTTPD) showed poor power conversion efficiency (PCE, 1.14 and 1.25%) because of the very low short-circuit current density (JSC). The voltage-dependent photocurrent and photoluminescence quenching measurements suggested that hole transfer from PC71BM to polymer depends strongly on the HOMO level of the polymer. The PCTTPD and PCTTTPD devices suffered from electron-hole recombination at the polymer/PC71BM interfaces because of the insufficient energy offset between the HOMOs of the polymer and PC71BM. The PCBTTPD:PC71BM device showed the best PCE of 3.42% with a VOC and JSC of 0.86 V and 7.79 mA cm-2, respectively. These results show that photovoltaic polymers should be designed carefully to have a deep HOMO level for a high VOC and sufficient energy offset for ensuring efficient hole transfer from PC71BM to the polymer.
AB - Three kinds of donor-acceptor (D-A) type photovoltaic polymers were synthesized based on 2,7-carbazole and thieno[3,4-c]pyrrole-4,6-dione (TPD). The conjugation of weakly electron (e)-donating 2,7-carbazole and strongly e-accepting TPD moieties yielded a deep highest occupied molecular orbital (HOMO) and its energy level was fine-controlled to be -5.72, -5.67 and -5.57 eV through the incorporation of thiophene (T), thieno[3,2-b]thiophene (TT) and bithiophene (BT) as a π-bridge. Polymer:[6,6]-phenyl-C71 butyric acid methyl ester (PC71BM) based bulk heterojunction solar cells exhibited a high open-circuit voltage (VOC) in the range, 0.86-0.94 V, suggesting good agreement with the measured HOMO levels. Despite the high VOC, the thiophene (or thienothiophene)-containing PCTTPD (or PCTTTPD) showed poor power conversion efficiency (PCE, 1.14 and 1.25%) because of the very low short-circuit current density (JSC). The voltage-dependent photocurrent and photoluminescence quenching measurements suggested that hole transfer from PC71BM to polymer depends strongly on the HOMO level of the polymer. The PCTTPD and PCTTTPD devices suffered from electron-hole recombination at the polymer/PC71BM interfaces because of the insufficient energy offset between the HOMOs of the polymer and PC71BM. The PCBTTPD:PC71BM device showed the best PCE of 3.42% with a VOC and JSC of 0.86 V and 7.79 mA cm-2, respectively. These results show that photovoltaic polymers should be designed carefully to have a deep HOMO level for a high VOC and sufficient energy offset for ensuring efficient hole transfer from PC71BM to the polymer.
KW - Carbazole
KW - Charge recombination
KW - Photovoltaic polymer
KW - Polymer solar cell
KW - Thienopyrroledione
UR - http://www.scopus.com/inward/record.url?scp=84925358689&partnerID=8YFLogxK
U2 - 10.1016/j.cap.2015.02.019
DO - 10.1016/j.cap.2015.02.019
M3 - Article
AN - SCOPUS:84925358689
SN - 1567-1739
VL - 15
SP - 654
EP - 661
JO - Current Applied Physics
JF - Current Applied Physics
IS - 5
ER -
