Poly(3-n-butylthiophene) (P3BT) samples with different average molecular weights and headto-tail regioregularity were crystallized in the form II crystal polymorph either from solution or by annealing with CS 2 vapors. With a combined approach, making also use of literature electron diffraction data, we show that form II is well described by a limit-ordered monoclinic model in space group P2 1 /c with lattice parameters a = 10.76(1) A ˚, b = 7.77(1) A ˚(chain axis), c = 9.44(1) A ˚, and β = 64.66°, yielding a calculated density of 1.29 g/cm 3 in qualitative agreement with proposals by Winokur et al. for the form II structures of regioregular poly(3-octylthiophene) and poly(3-dodecylthiophene) (P3DDT). Our structural model was refined by Rietveld analysis and has been confirmed by molecular mechanics (MM) and molecular dynamics (MD) calculations adopting a thiophene-specific force field developed in our group. Consistent with its higher density and with thermal data, form II shows lower potential energy than the form I 0 crystalline polymorph of P3BT. Both the main-chain and the side-chain conformations closely correspond to those found in form I 0 polymorph. The form II P3BT refined structural model presents an antidirectional looser stacking and tightly interdigitated layering, different from those observed in the form I family of poly(3-alkythiophenes) (P3ATs) and crystallite dimension of 20-30 A ˚along the chain axis. This feature and the lamellar structure implied by the spherulitic morphology are consistent with substantial chain-folding for high molecular weight samples. Oriented X-ray diffraction patterns from thin films of form II P3BT are explained assuming that the stacking axis c, corresponding to the radial, fast growth direction of the bidimensional form II spherulites, is preferentially in the plane of the film, while the layer axis a and the chain axis b approach random orientation around c, at variance with recent literature suggestions. The small crystal dimensions along the chain axis, the looser stacking, the relevance of chain folding and the spherulitic morphology implying film discontinuity suggest that the form II structural family of P3AT's are less viable than the form I polymorphs for molecular electronics applications.

The replacement of common fullerene derivatives with neat-C70 could be an effective approach to restrain the costs of organic photovoltaics and increase their sustainability. In this study, bulk-heterojunction solar cells made of neat-C70 and low energy-gap conjugated polymers, PTB7 and PCDTBT, are thoroughly investigated and compared. Upon replacing PC70BM with C70, the mobility of positive carriers in the donor phase is roughly reduced by 1 order of magnitude, while that of electrons is only slightly modified. It is shown that the main loss mechanism of the investigated neat-C70 solar cells is a low mobility-lifetime product. Nevertheless, PCDTBT:C70 devices undergo a limited loss of 7.5%, compared to the reference PCDTBT:PC70BM cells, reaching a record efficiency (4.44%) for polymer solar cells with unfunctionalized fullerenes. The moderate efficiency loss of PCDTBT:C70 devices, due to an unexpected excellent miscibility of PCDTBT:C70 blends, demonstrates that efficient solar cells made of neat-fullerene are possible. The efficient dispersion of C70 in the PCDTBT matrix is attributed to an interaction between fullerene and the carbazole unit of the polymer.

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Stability is the main challenge in the field of organic-inorganic perovskite solar cells (PSCs). Finding low-cost and stable hole transporting layer (HTL)is an effective strategy to address this issue. Here, a new donor polymer, poly(5,5-didecyl-5H-1,8-dithia-as-indacenone-alt-thieno[3,2-b]thiophene) (PDTITT), is synthesized and employed as an HTL in PSCs, which has a suitable band alignment with respect to the double-A cation perovskite film. Using PDTITT, the hole extraction in PSCs is greatly improved as compared to commonly used HTLs such as 2,2′,7,7′-tetrakis[N,N-di(4-methoxyphenyl) amino]-9,9′-spirobifluorene (spiro-OMeTAD), addressing the hysteresis issue. After careful optimization, an efficient PSC is achieved based on mesoscopic TiO 2 electron transporting layer with a maximum power conversion efficiency (PCE) of 18.42% based on PDTITT HTL, which is comparable with spiro-OMeTAD-based PSC (19.21%). Since spiro-based PSCs suffer from stability issue, the operational stability in the PSC with PDTITT HTL is studied. It is found that the device with PDTITT retains 88% of its initial PCE value after 200 h under illumination, which is better than the spiro-based PSC (54%).the stability is the main challenge in the PSCs, which is a key step for commercialization of these devices. [19][20][21] One of the main reasons for the instability of PSCs is the hole transporting layer (HTL) materials, which can be addressed properly by using new alternative HTLs. [22][23][24] One of the most commonly used HTLs in the PSCs is 2,2′,7,7′-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9′-spirobifluorene (spiro-OMeTAD), which is a great choice for the fabrication of highly efficient PSC over 23%. [5,25] However, the PSCs based on Spiro-OMeTAD suffer from poor stability due to the presence of unstable dopants as well as many voids through the HTL. In order to address this issue, compositional engineering by adding new additives into the molecular structure of spiro or interface engineering by adding an extra layer on top of the spiro could be potential solutions. [25][26][27][28][29] For example, Sunehira et al. [30] applied a thin layer of MoO 3 between spiro and electrode, resulting in an efficient PSC with better stability.These strategies improved the stability of the PSCs slightly and could not be an ideal solution for this issue. Consequently, replacement of spiro-OMeTAD using new stable HTLs is a better choice to improve the stability of the PSCs. There are many organic and inorganic HTLs for replacing spiro, however, they are expensive such as poly(triaryl amine) PTAA, require high-temperature annealing such NiO, or show limited efficiency and stability. [31][32][33][34][35] In this work, we synthesize a new and low-cost donor polymer, poly(5,5-didecyl-5H-1,8-dithia-as-indacenone-altthieno[3,2-b]thiophene) (PDTITT), and employ it as a potential HTL for the fabrication of efficient and stable PSCs. Our proposed polymer is cheaper than commonly used HTL polymers such as spiro and PTAA, thanks to its lower synthesis complexity, ...

Low carrier mobility and lifetime in semiconductor polymers are some of the main challenges facing the field of organic photovoltaics (OPV) in the quest for efficient devices with high current density. Finding novel strategies such as device structure engineering is a key pathway toward addressing this issue. In this work, the light absorption and carrier collection of OPV devices are improved by employment of ZnO nanowire (NW) arrays with an optimum NW length (50 nm) and antireflection (AR) film with nanocone structure. The optical characterization results show that ZnO NW increases the transmittance of the electron transporting layer as well as the absorption of the polymer blend. Moreover, the as‐deposited polymer blend on the ZnO NW array shows better charge transfer as compared to the planar sample. By employing PC70BM:PV2000 as a promising air‐stable active‐layer, power conversion efficiencies of 9.8% and 10.1% are achieved for NW devices without and with an AR film, indicating 22.5% and 26.2% enhancement in PCE as compared to that of planar device. Moreover, it is shown that the AR film enhances the water‐repellent ability of the OPV device.