•High-performance C60 based OTFTs with low operation voltage.•Low-cost Cu modified by PEI as S/D electrodes.•Electron mobility up to 3.2 cm2/V s is obtained on modified device.•Improved interface property between Cu and C60 upon interface modification.Exploring suitable electrode materials with sufficiently low work function, ambient stability and low-cost is of great technological importance to the development of n-channel OTFTs. Here, we show that the work function of Cu can be effectively reduced from 4.65 eV to 4.28 eV through surface modification via simply spin-coating a thin layer of branched polyethylenimine (PEI). By exploiting a high-capacitance density gate dielectric (200 nF/cm2), low-voltage (3 V) C60 TFTs with electron mobility (μe) of 3.2 cm2/V s are demonstrated with PEI modified Cu as source–drain (S/D) electrodes. In contrast, the device with Cu S/D electrodes possesses μe of only 1.0 cm2/V s. The improvement in electrical performance of the PEI modified device is attributed to the efficient electron injection at the Cu/C60 interface which resulted from the reduction in work function of Cu. Moreover, upon PEI modification, the bias stability of the device can be obviously enhanced as compared to the unmodified one, and the resultant device exhibits an excellent thermal stability up to 200 °C without appreciable degradation in mobility. The facile modification of low-cost Cu as S/D electrodes for high-performance n-channel OTFTs as well as the low-voltage operation will pave the way for large scale manufacturing of organic electronics.

•Solar cell performance enhanced by adding dichloromethane to 1,2 o-dichlorobenzene.•The crystallization of P3HT increased in competing solvent evaporation process.•The film surface composition was tuned from P3HT-rich to more favored PCBM-rich.•The charge transfer at the active layer-cathode interface was optimized.In this work, the effects of mixed solvents on donor–acceptor vertical phase separation and light absorption was investigated. By using mixed orthogonal solutions of 1,2 o-dichlorobenzene (o-DCB) and dichloromethane (DCM), a PCBM([6,6]-phenyl-C61-butyric acid methyl ester)-rich top layer was induced in typical poly(3-hexylthiophene-2,5-diyl)(P3HT):PCBM bulk heterojunction structure. By carefully adjusting the o-DCB:DCM volume ratio, the contact between active layer and the Al cathode was significantly improved due to the precipitation of PCBM on the top surface, which resulting in an electron transport preferable interface between the active layer and cathode. Meanwhile, light absorption was also effectively improved due to the increased crystallinity of polymers under mixed solvents. Overall, the short circuit current was greatly increased, and the efficiency was improved from 3.07% in the control sample to 3.97% by adding 30% DCM. The detailed mechanism of the formation of PCBM-rich layer and enhanced light absorption with o-DCB:DCM solution was expatiated. Our findings suggest a facile spin coating method to fabricate efficient BHJ solar cells, which can pave the way for the large scale application of organic photovoltaic devices (OPVs) in the future.Graphical abstract

We demonstrate low-voltage pentacene thin film transistors (TFTs) using in situ modified low-cost Cu (M-Cu) as source–drain (S/D) electrodes and solution-processed high capacitance (200 nF/cm2) gate dielectrics. Under a gate voltage of −3 V, the device with M-Cu electrodes shows a much higher apparent mobility (1.0 cm2/V s), a positively shifted threshold voltage (−0.62 V), a lower contact resistance (0.11 MΩ) and a larger transconductance (12 μS) as compared to the device with conventional Au electrodes (corresponding parameters are 0.71 cm2/V s, −1.44 V, 0.41 MΩ, and 5.7 μS, respectively). The enhancement in the device performance is attributed to the optimized interface properties between S/D electrodes and pentacene. Moreover, after encapsulation the M-Cu electrodes with a thin layer of Au in the aim of suppressing unfavorable surface oxidation, the electronic characteristics of the device are further improved, and highly enhanced apparent mobility (2.3 cm2/V s) and transconductance (19 μS) can be achieved arising from the increased conductivity of the electrode itself. Our study provides a simple and feasible approach to achieve high performance low-voltage OTFTs with low-cost S/D electrodes, which is desirable for large area applications.Graphical abstractHighlights► Low-voltage pentacene OTFTs with solution-processed dielectric. ► In situ modification of low-cost Cu (M-Cu) as S/D electrodes. ► M-Cu based device show higher performance than Au and Cu. ► Mobility reaches 2.0 cm2/V s with Au encapsulated M-Cu (Au/M-Cu) electrodes. ► The mechanism of this phenomenon is studied in detail.