Although conventional laser ablation (CLA) method has widely been used in patterning of organic semiconductor thin films, its quality control still remains unsatisfied due to the ambiguous photochemical and photothermal processes. Based on industrial available near-infrared laser source, herein, a novel “layer-filter threshold” (LFT) technique is proposed, which involves the decomposition of targeted “layer-filter” and subsequent explosive evaporation process to purge away the upper layers instead of layer-by-layer ablation. For photovoltaic device with structure of metal/blend/PEDOT:PSS/ITO/glass, the PEDOT:PSS layer as the “layer-filter” is first demonstrated to be effective, and then the merged P1–P2 line and metal electrode layer are readily patterned through the “self-aligned” effect and regulation of ablation direction, respectively. The correlation between laser fluence and explosive ablation efficacy is also investigated. Finally, photovoltaic modules based on classical P3HT:PC₆₁BM and low-bandgap PBDT-TFQ:PC₇₁BM systems are separately fabricated following the LFT technique. It is found that over 90% of geometric fill factor is achieved while device performances maintain in a limited change with increased number of series cells. In comparison to conventional laser ablation methods, the LFT technique does not require sophisticated instruments but reaches comparable processing accuracy, which shows promising potential in the fabrication and commercialization of organic semiconductor thin-film devices.

A combination of patterning and film alignment techniques helps to build multi-order polymer architecture for application in flexible electronics. A direct-writing method is employed using microcapillary arrays to prepare semiconducting polymer films with both optical and electrical anisotropy. Not only aligned poly(3-butylthiophene) (P3BT) nanowires in neat P3BT films, but also aligned P3BT nanowires within a polystyrene (PS) matrix are obtained, which yields an aligned semiconductor/insulator polymer blend with anisotropic charge transport. The field-effect transistor (FET) mobilities/threshold voltages from both vertical and parallel to alignment directions as well as their dependence on blending ratio are studied. The increased mobility of P3BT/PS blends, as compared with neat P3BT, is observed in both vertical and parallel directions. Using this alignment method, FET mobility and threshold voltage of the semiconductor/insulator polymer blends are comprehensively tuned, from which a digital inverter with gain up to 80 is realized. Therefore, this work not only helps understanding the charge transport mechanism in semiconducting/insulating polymer blends, but also provides an effective approach towards high-performance field-effect transistors with tunable mobility and threshold voltage.

A series of block copolymers with fixed length of the semiconductor-block poly(3-butylthiophene) (P3BT) and varying length of the insulator-block polystyrene (PS) are synthesized. These copolymers are blended with phenyl-C61-butyric acid methyl ester (PCBM) for the bulk heterojunction photoactive layers. With appropriate insulator-block length and donor–acceptor ratio, the power conversion efficiency increases by one order of magnitude compared with reference devices with pure P3BT/PCBM. PS blocks improve the miscibility of the active layer blends remarkably. The P3BT-b-PS crystallizes as nanorods with the P3BT core covered with the PS-block, which creates a nanoscale tunneling barrier between donor and acceptor leading to more efficient transportation of charge carriers in the semiconductors.

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 (M_n). The devices based on PDTSTPD/PC₇₁BM composite are prepared and the dependence of power conversion efficiency (PCE) of the devices on the M_n of conjugated polymers is addressed. We found the hole mobility of PDTSTPD is dependent on the M_n 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.

The charge transportation in poly(3-butylthiophene) (P3BT)/insulating polymer composites is studied both microscopically and macroscopically. The increased mobility of free charge carriers, in particular hole mobility, contributes to the enhanced electrical conductivity of this semiconductor/insulator composite. The conductivity origin of the composite, as revealed by conductive-atomic force microscopy (C-AFM), comes mainly from the P3BT network, whose carrier mobility has been improved as a result of reduced activation energy for charge transportation upon forming an interface with the insulating matrix. Both the huge interfacial area and interconnected conductive component are morphologically required for the enhanced electrical property of the composite. An increased size of the P3BT domains, which correspondingly reduces the interfacial area between the two components, ruins the enhancement. This study clarifies the mechanism of the higher electrical properties achieved in a semiconducting polymer upon blending with an insulating polymer, which will further promote the development of these low-cost, easily processable, and environmentally stable composites.