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Abstract: Recently, the influence of molecular weight (Mn) on the performance of polymer solar cells (PSCs) is widely investigated. However, the dependence of optimal thickness of active layer for PSCs on Mn is not reported yet, which is vital to the solution printing technology. In this work, the effect of Mn on the efficiency and especially optimal thickness of the active layer for PBTIBDTT‐S‐based PSCs is systematically studied. The device efficiency improves significantly as the Mn increases from 12 to 38 kDa, and a remarkable efficiency of 10.1% is achieved, which is among the top efficiencies of wide‐bandgap polymer:fullerene PSCs. Furthermore, the optimal thickness of the active layer is also greatly increased from 62 to 210 nm with increased Mn. Therefore, a device employing a thick (>200 nm) active layer with power conversion efficiency exceeding 10% is achieved by manipulating Mn. This exciting result is attributed to both the improved crystallinity, thus hole mobility, and preferable polymer orientation, thus morphology of active layer. These findings, for the first time, highlight the significant impact of Mn on the optimal thickness of active layer for PSCs and provide a facile way to further improve the performance of PSCs employing a thick active layer. [ABSTRACT FROM AUTHOR]

Abstract: Currently, constructing ternary organic solar cells (OSCs) and developing nonfullerene small molecule acceptors (n‐SMAs) are two pivotal avenues to enhance the device performance. However, introducing n‐SMAs into the ternary OSCs to construct thick layer device is still a challenge due to their inferior charge transport property and unclear aggregation mechanism. In this work, a novel wide band gap copolymer 4,8‐bis(4,5‐dioctylthiophen‐2‐yl) benzo[1,2‐b:4,5‐b′]dithiophene‐2,6‐diyl‐alt‐N‐(2‐hexyldecyl)‐5,5′‐bis(thiophen‐2‐yl)‐2,2′‐bithiophene‐3,3′‐dicarboximide (PDOT) is designed and blend of PDOT:PC71BM achieves a power conversion efficiency (PCE) of 9.5% with active layer thickness over 200 nm. The rationally selected n‐SMA based on a bulky seven‐ring fused core (indacenodithieno[3,2‐b]thiophene) end‐capped with 2‐(3‐oxo‐2,3‐dihydroinden‐1‐ylidene) malononitrile groups (ITIC) is introduced into the host binary PDOT:PC71BM system to extend the absorption range and reduce the photo energy loss. After fully investigating the morphology evolution of the ternary blends, the different aggregation behavior of n‐SMAs with respect to their fullerene counterpart is revealed and the adverse effect of introducing n‐SMAs on charge transport is successfully avoided. The ternary OSC delivers a PCE of 11.2% with a 230 nm thick active layer, which is among the highest efficiencies of thick layer OSCs. The results demonstrate the feasibility of using n‐SMAs to construct a thick layer ternary device for the first time, which will greatly promote the efficiency of thick layer ternary devices. [ABSTRACT FROM AUTHOR]

Abstract: In the past decade, the power conversion efficiencies (PCEs) of polymer solar cells (PSCs) have been improved significantly. However, most efficient PSCs are based on halogenated solvents and the spin‐coating technique. To meet the requirements of practical fabrication, PSCs processed from non‐halogenated solvents using scalable deposition techniques are required. In this work, a non‐halogenated solvent system, o‐xylene/benzyl phenyl ether (BPE), was utilized to fabricate PSCs. The PSC obtained through spin coating from o‐xylene/BPE exhibited a high PCE comparable to a PCE spin‐coated from halogenated solvent. The nanostructures of the films processed from different solvents were investigated systematically to understand their performance evolution. Importantly, a spray‐coating technique compatible with the roll‐to‐roll process was employed to fabricate PSCs using an eco‐compatible ink formulation. The PSC spray coated from o‐xylene/BPE in ambient atmosphere gave rise to a PCE of 7.74 % comparable to that of devices spin‐coated from halogenated solvents, which demonstrated a significant potential for further practical fabrication. [ABSTRACT FROM AUTHOR]

A new crystallizable low band gap conjugated copolymer BTT ‐ DTFFBT is designed and synthesized. The polymer solar cells based on BTT ‐ DTFFBT: PC71BM photoactive layer are fabricated and characterized. It is found that after combined treatment of 1 vol % 1 ‐ chloronaphthalene (CN) additive and thermal annealing at 180 °C for 10 min, the device shows a power conversion efficiency (PCE) of 5.61% and good thermal stability. [ABSTRACT FROM AUTHOR]

A series of brominated polystyrenes (BPSs) are readily synthesized and blended as polymer dopants with the p-type semiconducting polymer, poly(3-hexylthiophene) (P3HT), to improve theirelectrical performance. The obtained P3HT/BPS blend films exhibit increased carrier concentration resulting from doping of P3HT by BPS, which leads to excellent electrical performance, including enhanced hole mobility and conductivity, and the conductivity or mobility increases with the bromination degree of BPS. Compared with conventional small molecular dopants, the polymer dopant, BPS, shows not only excellent doping stability, but also good solution processibility, which makes it a promising materials for fabrication of low cost, flexible, transparent, and high performance solution processable organic electronic devices. [ABSTRACT FROM AUTHOR]

In this work, we synthesized a low bandgap polymer polysilole(-2,6-diyl-alt-5-octylthieno[3,4- c]pyrrole-4,6-dione) (PDTSTPD) with different molecular weights ( Mn). The devices based on PDTSTPD/PC71BM composite are prepared and the dependence of power conversion efficiency (PCE) of the devices on the Mn of conjugated polymers is addressed. We found the hole mobility of PDTSTPD is dependent on the Mn of the polymer, which should be the main reason contributing to the drastic difference of device performance, i.e. the PCE of the device using 10 kDa polymer is only 0.52%, in contrast to 2.3% for 24 kDa polymer device. This PCE data is then further improved to 5.0% via using 1,8-diiodoctane as processing additive to achieve an optimized morphology for the photoactive layer with an appropriate length-scale of phase separation for both exciton dissociation and charge transportation. [ABSTRACT FROM AUTHOR]