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Overcoming Fill Factor Reduction in Ternary Polymer Solar Cells by Matching the Highest Occupied Molecular Orbital Energy Levels of Donor Polymers
Author(s) -
Lee Jihoon,
Tamilavan Vellaiappillai,
Rho Kyung Hwan,
Keum Sangha,
Park Ki Hong,
Han Daehee,
Jung Yun Kyung,
Yang Changduk,
Jin Youngeup,
Jang JaeWon,
Jeong Jung Hyun,
Park Sung Heum
Publication year - 2018
Publication title -
advanced energy materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 10.08
H-Index - 220
eISSN - 1614-6840
pISSN - 1614-6832
DOI - 10.1002/aenm.201702251
Subject(s) - ternary operation , materials science , homo/lumo , polymer solar cell , band gap , polymer , energy conversion efficiency , open circuit voltage , thiophene , polymer chemistry , organic chemistry , optoelectronics , molecule , voltage , chemistry , composite material , physics , computer science , programming language , quantum mechanics
Abstract Despite the potential of ternary polymer solar cells (PSCs) to improve photocurrents, ternary architecture is not widely utilized for PSCs because its application has been shown to reduce fill factor (FF). In this paper, a novel technique is reported for achieving highly efficient ternary PSCs without this characteristic sharp decrease in FF by matching the highest occupied molecular orbital (HOMO) energy levels of two donor polymers. Our ternary device—made from a blend of wide‐bandgap poly[4,8‐bis(2‐ethylhexyloxy)benzo[1,2‐b:4,5‐b′]dithiophene‐alt‐2,5‐dioctyl‐4,6‐di(thiophen‐2‐yl)pyrrolo[3,4‐c]pyrrole‐1,3(2H,5H)‐dione) (PBDT‐DPPD) polymer, narrow‐bandgap poly[4,8‐bis[5‐(2‐ethylhexyl)‐2‐thienyl]benzo[1,2‐b:4,5‐b′]dithiophene‐alt‐(4‐(2‐ethylhexyl)‐3‐fluorothieno[3,4‐b]thiophene‐)‐2‐carboxylate‐2‐ 6‐diyl)] (PTB7‐Th) polymer, and [6,6]‐phenyl C 70 ‐butyric acid methyl ester (PC 70 BM)—exhibits a maximum power conversion efficiency of 10.42% with an open‐circuit voltage of 0.80 V, a short‐circuit current of 17.61 mA cm −2 , and an FF of 0.74. In addition, this concept is extended to quaternary PSCs made by using three different donor polymers with similar HOMO levels. Interestingly, the quaternary PSCs also yield a good FF (≈0.70)—similar to those of corresponding binary PSCs. This study confirms that the HOMO levels of the polymers used on the photoactive layer of PSCs are a crucial determinant of a high FF.