Ching Ting

Low-bandgap poly(thiophene-phenylene-thiophene) derivatives with broaden absorption spectra for use in high-performance bulk-heterojunction polymer solar cells.

Two low-bandgap (LGB) conjugated polymers ( P1 and P2) based on thiophene-phenylene-thiophene (TPT) with adequate energy levels have been designed and synthesized for application in bulk-heterojunction polymer solar cells (PSCs). The absorption spectral, electrochemical, field effect hole mobility and photovoltaic properties of LGB TPT derivatives are investigated and compared with poly(3-hexylthiophene) (P3HT). Photophysical studies reveal bandgaps of 1.76 eV for P1 and 1.70 eV for P2, which could effectively harvest broader solar spectrum. In addition, the thin film absorption coefficients of P1 and P2 are 1.6 x 10 (5) cm (-1) (lambda approximately 520 nm) and 1.4 x 10 (5) cm (-1) (lambda approximately 590 nm), respectively. Electrochemical studies indicate desirable HOMO/LUMO levels that enable a high open circuit voltage while blending them with fullerene derivatives as electron acceptors. Furthermore, both materials show sufficient hole mobility (3.4 x 10 (-3) cm (2)/Vs for P2) allowing efficient charge extraction and a good fill-factor for PSC application. High-performance power conversion efficiency (PCE) of 4.4% is obtained under simulated solar light AM 1.5 G (100 mW/cm (2)) from PSC device with an active layer containing 25 wt% P2 and 75 wt% [6,6]-phenyl-C71-butyric acid methyl ester (PC 71BM), which is superior to that of the analogous P3HT cell (3.9%) under the same experimental condition.

Cu(I) chelated poly-alkoxythiophene enhancing photovoltaic device composed of a P3HT/PCBM heterojunction system

We report the Cu+ chelated poly-alkoxythiophene (P3MEET) enhancement of a solar cell device consisting of a P3HT/PCBM heterojunction system. Compared to the reference P3HT/PCBM system, a consistent increase of conversion efficiency of 0.9% via an apparent increase of incident-photon-to-current conversion efficiency (IPCE) is achieved upon optimizing the ratio of P3MEET-Cu+ : P3HT : PCBM to 1 : 9 : 6 by weight, in which 7.5 mol% of CuBr is added upon synthesizing P3MEET-Cu+. The results, in combination with relevant data gathered from atomic force microscopy, cyclic voltammetry, and electrochemical impedance spectra, lead us to conclude that the match in redox potential and increase of ordering of the film upon doping P3MEET-Cu+ play two key roles in enhancing the performance.

Effective Light Harvesting of Tandem Polymer Solar Cell

A novel soluble conjugated polymers, P2, with coplanar thiophene-phenylene-thiophene unit is designed and synthesized as suitable active material used in tandem cells to compensate the poly(3-hexylthiophene) (P3HT)/[6.6]-phenyl-C71 butyric acid methyl ester (PC 71 BM) bulk-heterojunction cell in this paper. P2 polymer bears advantages in both low optical bandgap (1.7 eV) and high hole mobility properties (3.4 ×10 ―3 cm 2 /V-s from field-effect transistor measurement). Furthermore, the electrochemical studies of P2 indicate desirable highest occupied molecular orbital/lowest unoccupied molecular orbital (HOMO/LUMO) band structure that enables a high open circuit voltage when pairing with PCBM acceptor. The best power conversion efficiency of this polymer solar cell thus far based on P2/PC 71 BM system with a weight ratio of 1:3 reached 4.4% with a short circuit current density (J sc ) of 10.2 mA/cm 2 , an open circuit voltage (V oc ) of 0.81 V, and a fill factor (FF) of 0.53 under air mass (AM) 1.5 G (100 mW/cm 2 ). The preliminary data of the tandem cell with indium tin oxide (ITO) glass/PEDOT:PSS/P2: PC 7 /BM/TiOx/PEDOT: PSS/P3HT: PC 7 /BM/TiOx/Al configuration has reached J sc of 6.2 mA/cm 2 , V oc of 1.33 V, FF of 0.56 and an overall efficiency of 4.6% under AM 1.5 G (100 mW/cm 2 ).