Polymer-blend solar cells (all-PSCs) based on a copolymer of naphthodithiophene diimide and bithiophene (PNDTI-BT-DT) as a near-infrared absorber as well as an electron acceptor were fabricated in combination with PTB7 as an electron donor. Notably, the external quantum efficiency spectra of the all-PSCs demonstrated photoresponse up to 900 nm with the efficiency of 25% at 800 nm, which is much higher than that for the previously reported all-PSCs. Power conversion efficiency as high as 2.59% was achieved under the irradiation of simulated solar light (AM1.5, 100 mW/cm2). Both PNDTI-BT-DT and PTB7 formed a crystalline structure in the blend films similar to in the pristine films, leading to the efficient charge generation contributed from both polymers.

By introducing different numbers of thienyl spacers, the properties of D–A type polymers could be modulated, which provides a simple strategy for designing high-performance D–A type photovoltaic polymers based on the existing polymers.

A power conversion efficiency of 3.6% for an all-polymer solar cell, which is the highest ever reported, is achieved by introducing a conjugated side chain into a p-type polymer to improve the miscibility of the polymer blend and by adding small amounts of 1,8-diiodooctane to increase the aggregation of n-type polymer.

A novel alternating copolymer with a low band gap (E-g = 1.55 eV), PBDT-DTBSe, based on benzodithiophene (BDT) and benzoselenadiazole (BSe) units with thiophene as a pi-conjugated bridge, was synthesized and characterized. When 1,8-diiodooctane was used as a solvent additive to optimize the mixing morphology, the maximum power conversion efficiency reached by a polymer solar cell based on PBDT-DTBSe/PC70BM was 5.18%, which was slightly higher than that of the benzothiadiazole (BT)-based analogue (5.01%). These results demonstrated the promising effectiveness of benzoselenadiazole as an electron-deficient unit for the design of the donor acceptor photovoltaic polymers.

We report a simple, effective approach to modifying two kinds of D–A type polymers; copolymerization with thiophene containing tris(thienylenevinylene) (TTV) conjugated side chain. The resulting copolymers, TTV1 and TTV2, showed significant improvement (25% and 43%) of power conversion efficiency in comparison to the original polymers. The short-circuit current of TTV2 reached 22.6 mA cm−2 that is the highest record for organic photovoltaic devices to date. This design strategy opens up a new possibility to modify the existing D–A type photovoltaic polymers for better performance.

A new alternating copolymer of fluorene and naphthalene diimide, PF-NDI, was synthesized and characterized. The highest power conversion efficiency of all-polymer solar cells based on P3HT: PF-NDI reached 1.63% with a relatively high fill factor of 0.66 by using 1,8-diiodooctane as a solvent additive to optimize the mixing morphology.

It′s all about polymers: All-polymer solar cells (all-PSCs) based on six perylene diimide containing polymers (PX–PDIs) as acceptor materials and two polythiophene derivatives (P3HT and PT1) as donor materials were investigated systematically (see picture). The highest power-conversion efficiency (PCE) of all-PSCs was 2.23 %, one of the highest PCEs of polymer/polymer blend photovoltaic devices reported to date.

Two kinds of thieno[3,4-b]pyrazine-based monomers, 2,3-dimethyl-5,7-di(2-bromothien-5-yl)-thieno[3,4-b]pyrazine and 2,3-dipheliyl-5,7-di(2-bromothien-5-yl)-thietlo[3,4-b]pyrazine, were synthesized via an improved synthetic route. These two monomers and 4,7-di(2-brothothien-5-yl)-2,1,3-benzothiadiazole were copolymerized with three donor segments (fluorene, carbazole, and indolocarbazole) separately by a Suzuki cross-coupling reaction to give six types of 5,7-dithien-2-yl-thieno[3,4-h]pyrazine (DTTP)-based donor-acceptor (D-A) copolymers (TPI-6) and three types of 5,7-dithien-2-yl-2,1,3-benzitguaduazole (DTBT)-based D-A copolymers (PF-DTBT, PC-DTBT, and PIC-DTBT). The optical properties, electrochemical behavior, and energy levels of these nine copolymers were investigated. The photovoltaic performance of the copolymers was compared and discussed considering their energy levels.

Four donor acceptor (D-A) type copolymers, namely, poly{9,9-dioctylfluorene-2,7-diyl-alt-5-8-dithien-2-yl-2,3-dephenylquinoxaline-5,5',5 ''-diyl}(PF-DTQx), poly{N-[1-(2'-ethylhexyl)-3-ethyl-heptanyl]carbazole-2,7-diyl-alt-5,8-dithien-2-yl-2,3-diphenylquinoxaline-5',5 ''-diyl} (PC-DTQx), poly{5,11-di(1-decylundecyl)indolo[3,2-b]carbazole-3,9-diyl-alt-5,8-dithien-2-yl-2,3-diphenylquinoxaline-5',5 ''-diyl} (PIC-DTQx), and poly{N-[1-(2'-ethylhexyl)-3-ethylheptanyl]-dithieno[3,2-b:2',3'-d]-pyrrole-2,6-diyl-alt-5,8-dithien-2-yl-2,3-diphenylquinoxaline-5',5 ''-diyl} (PDTP-DTQx), were synthesized by Suzuki or Stille coupling reactions. By changing the donor segment, the band gaps and energy levels of these 5,8-dithien-2-yl-2,3-diphenylquinoxaline (DTQx)-based polymers could be finely tuned. PDTP-DTQx exhibited the narrowest band gap of 1.56 eV and the absorption edge extended to 770 nm. We investigated bulk heterojunction type polymer solar cells (PSCs) based on these copolymers as the electron donor materials, and [6,6]-phenyl C-61 butyric acid methyl ester (PCBM) or [6,6]-phenyl C-71 butyric acid methyl ester (PC70BM) as the acceptor. The power conversion efficiency (PCE) of the PSCs was in the range of 1.17-3.23% under AM 1.5 illumination (100 mW/cm(2)).

A novel donor-acceptor (D-A) type alternating copolymer based on dithieno[3,2-b:2',3'-d]pyrrole (DTP) and thieno[3,4-c]pyrrole-4,6-dione (TPD) was synthesized. The polymer has a broad absorption spectrum in the range of 350-810 nm. The energy levels of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of the copolymer were -5.11 and -3.63 eV, respectively, as determined by cyclic voltammetry. Bulk heterojunction type polymer solar cells based on PDTP-TPD and PC70BM, showed power conversion efficiency (PCE) up to 1.6% with an open-circuit voltage of V-OC = 0.66 V, a short-circuit current of I-SC = 4.98 mA.cm(-2), and a fill factor of FF = 0.50. The V-OC of 0.66 V is the highest value among DTP-based photovoltaic polymers.