Cesium tin halide based perovskite Cs 2 SnI 6 has been subjected to in-depth investigations owing to its potentiality toward the realization of environment benign Pb free and stable solar cells. In spite of the fact that Cs 2 SnI 6 has been successfully utilized as an efficient hole transport material owing to its p-type semiconducting nature, however, the nature of the majority carrier is still under debate. Therefore, intrinsic properties of Cs 2 SnI 6 have been investigated in detail to explore its potentiality as light absorber along with facile electron and hole transport. A high absorption coefficient (5 × 10 4 cm −1 ) at 700 nm indicates the penetration depth of 700 nm light to be 0.2 μm, which is comparable to conventional Pb based solar cells. Preparation of pure and CsI impurity free dense thin films with controllable thicknesses of Cs 2 SnI 6 by the solution processable method has been reported to be difficult owing to its poor solubility. An amicable solution to circumvent such problems of Cs 2 SnI 6 has been provided utilizing spray-coating in combination with spin-coating. The presence of two emission peaks at 710 and 885 nm in the prepared Cs 2 SnI 6 thin films indicated coexistence of quantum dot and bulk parts which were further supported by transmission electron microscopy (TEM) investigations. Time-resolved photoluminescence (PL) and transient absorption spectroscopy (TAS) were employed to investigate the excitation carrier lifetime, which revealed fast decay kinetics in the picoseconds (ps) to nanoseconds (ns) time domains. Time-resolved microwave photoconductivity decay (MPCD) measurement provided the mobile charge carrier lifetime exceeding 300 ns, which was also in agreement with the nanosecond transient absorption spectroscopy (ns-TAS) indicating slow charge decay lasting up to 20 μs. TA assisted interfacial charge transfer investigations utilizing Cs 2 SnI 6 in combination with ntype PCBM and p-type P3HT exhibited both intrinsic electron and hole transport.

Orienting semiconducting polymers (SCPs) using solution-processable techniques for organic electronic devices is essential for realizing a printable electronics device. Preparation of oriented films on liquid substrates and transferring on actual device substrate offers many advantages, including layer-by-layer coating, independent control of morphology, freedom to choose substrates, and device geometry. The floating films transfer method (FTM) has emerged as a unique method to prepare oriented films of SCP using solution processing. Here, we review recent progress in this method from the viewpoint of improvement in FTM to orient SCPs and their anisotropy in organic field effect transistors. In addition, the use of FTM films in sensing applications is also reviewed.

Large area (>20 cm × 2 cm)-oriented thin films of PQT-C12 with varying molecular weight and polydispersity index (PDI) were fabricated by the ribbonshaped floating film transfer method aiming toward their application as an active semiconductor element of organic field effect transistors (OFETs). Investigation on the influence of the molecular weight and PDI upon the extent of molecular alignment and anisotropic charge transport was systematically carried out. It has been demonstrated that high molecular weight in combination with low PDI not only leads to a very high optical anisotropy >10 but also high charge carrier anisotropy with a hole mobility of about 0.07 cm 2 /V•s for OFETs using parallel-oriented PQT-C12 thin films. Such a structure−property correlation is highly beneficial for the development of high performance organic electronic devices by synergistic and amicable tuning of the optoelectronic anisotropies and polymer synthetic variables.

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The role of film morphology of conjugated polymers (CPs) and their macromolecular conformation with respect to the substrate in governing charge transport and overall device performances has been a matter of debate. The nature of the macromolecular orientation of CPs in thin films has a pivotal role in controlling the performance of planar and sandwich devices. Thin-film characterizations unveiled that spin-coated films are isotropic with mixed edge-on/face-on conformation, whereas unidirectional floating film transfer method (UFTM) films are anisotropic with edge-on-oriented micrometer-sized ordered domains. To unravel the explicit role of molecular orientation on device performance, two types of devices, organic Schottky diodes (OSDs) for out-of-plane carrier transport and organic field-effect transistors (OFETs) for in-plane charge transport, were fabricated and characterized. Isotropic and relatively low crystalline spin-coated films exhibited superior transport characteristics in the out-ofplane direction than UFTM films irrespective of the crystallinity. On the other hand, edge-on-oriented UFTM thin films demonstrated remarkably enhanced in-plane charge transport with more than two orders of magnitude of enhancement in the fieldeffect mobility. The nature of molecular orientation of different films is significantly correlated with the performance of the OSDs and OFETs.