Polymer solar cells (PSCs) based on the bulk heterojunction (BHJ) blend of a conjugated polymer donor and a fullerene acceptor have gained considerable attention as a cost-effi cient, fl exible, and portable energy source. [1][2][3] Considering the practical aspects of its commercialization, the inverted device structure of PSCs (I-PSCs), consisting of a BHJ photoactive layer between indium tin oxide (ITO) as a bottom cathode and a high work function (WF) metal (Ag or Au) as a top anode, is an advantageous approach due to its superior long-term stability and printability. [4][5][6] In this type of inverted device structure, an additional interfacial layer between the active layer and ITO electrode must be introduced to establish the device concept. The high WF of the bottom ITO cathode (approximately 4.8 eV) hampers the formation of an ohmic contact with the lowest unoccupied molecular orbital (LUMO) level of fullerene and makes the creation of a high built-in fi eld used to break the electrical symmetry of the device diffi cult. Thus, many researchers explored a variety of interfacial materials to shift and modify the energy level of the ITO cathode. [4][5][6][7][8][9][10][11][12][13][14][15][16] Inorganic metal oxides (MOs), such as titanium oxide (TiO x ) or zinc oxide (ZnO), have been widely used as interfacial materials due to their solution processability (via a sol-gel precursor and nano-particle solutions) and their electron selective properties, which originate from their conduction band edges (typically at approximately 4 eV) that correspond well with the LUMO level of fullerene and the deep valence bands at approximately 8 eV. [8][9][10][11][12] However, I-PSCs using MOs typically require a high annealing temperature (over 200 ° C) to achieve a crystallinity of the MO that is suffi ciently high to yield a high charge carrier mobility, [ 8 , 9 ] and these devices require a crucial post-UV treatment to enhance the device performance (typically referred to as a 'light-soaking' problem). [10][11][12] Because the high-temperature annealing process is incompatible with typical printing processes that use fl exible plastic substrates and the post-UV treatment causes a harmful photo-oxidation in the conjugated polymers, these processes should be eliminated to promote the practical use of I-PSCs.To circumvent the inherent weaknesses of the MO interlayers, polymer-based interfacial materials, such as conjugated polyelectrolytes (CPEs) and nonconjugated polyethylene oxide (PEO), have also been employed. These polymer-based interlayers alter the WF of ITO by forming extremely thin interfacial dipoles (typically 1-2 nm) and facilitate charge transport into the ITO electrode. [17][18][19][20] Becuase cationic CPEs have charged ionic pendant groups in their structures, they can induce signifi cantly stronger dipole moments than the neutral PEO, resulting in a higher device performance than that of the I-PSC using PEO. [ 19 ] However, because CPEs typically require a delicate and complicated synthesis procedure, nonc...

Stretchable conductive materials have received great attention owing to their potential for realizing next-generation stretchable electronics. However, the simultaneous achievement of excellent mechanical stretchability and high electrical conductivity as well as cost-effective fabrication has been a significant challenge. Here, we report a highly stretchable and highly conducting polymer that was obtained by incorporating an ionic liquid. When 1-ethyl-3-methylimidazolium tetracyanoborate (EMIM TCB) was added to an aqueous conducting polymer solution of poly­(3,4-ethylenedioxythiophene):poly­(styrenesulfonate) (PEDOT:PSS), it was found that EMIM TCB acts not only as a secondary dopant but also as a plasticizer for PEDOT:PSS, resulting in a high conductivity of >1000 S cm–1 with stable performance at tensile strains up to 50% and even up to 180% in combination with the prestrained substrate technique. Consequently, by exploiting the additional benefits of high transparency and solution-processability of PEDOT:PSS, we were able to fabricate a highly stretchable, semitransparent, and wholly solution-processed alternating current electroluminescent device with unimpaired performance at 50% strain by using PEDOT:PSS/EMIM TCB composite films as both bottom and top electrodes.

Despite the recent unprecedented increase in the power conversion efficiencies (PCEs) of small-area devices (≤0.1 cm ), the PCEs deteriorate drastically for PSCs of larger areas because of the incomplete film coverage caused by the dewetting of the hydrophilic perovskite precursor solutions on the hydrophobic organic charge-transport layers (CTLs). Here, an innovative method of fabricating scalable PSCs on all types of organic CTLs is reported. By introducing an amphiphilic conjugated polyelectrolyte as an interfacial compatibilizer, fabricating uniform perovskite films on large-area substrates (18.4 cm ) and PSCs with the total active area of 6 cm (1 cm × 6 unit cells) via a single-turn solution process is successfully demonstrated. All of the unit cells exhibit highly uniform PCEs of 16.1 ± 0.9% (best PCE of 17%), which is the highest value for printable PSCs with a total active area larger than 1 cm .

The mechanical deflection of cantilever microbeams is presented as a new technique for testing the mechanical properties of thin films. Single-layer microbeams of Au and SiO2 have been fabricated using conventional silicon micromachining techniques. Typical thickness, width, and length dimensions of the beams are 1.0,20, and 30/j.m, respectively. The beams are mechanically deflected by a Nanoindenter, a submicron indentation instrument that continuously monitors load and deflection. Using simple beam theory and the load-deflection data, the Young's moduli and the yield strengths of thin-film materials that comprise the beams are determined. The measured mechanical properties are compared to those obtained by indenting similar thin films supported by their substrate.

The paired electric dipole layers significantly intensify the built-in field across the perovskite layer, resulting in suppressed charge trapping of photogenerated charges.