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Cu2SnS3 (CTS) is a promising compound for use as an absorber layer in thin‐film solar cells because it is made up of low‐cost and abundant elements. However, the band gap energy of 0.94 eV for monoclinic Cu2SnS3 is less than the optimal value for absorber layers in single‐junction solar cells. On the other hand, the band gap energy of Cu2GeS3 (CGS) is approximately 1.5–1.6 eV. Therefore, in this study, we carried out the synthesis of Cu2Sn1−xGexS3, which is a solid solution of Cu2SnS3 and Cu2GeS3. The structure of the prepared samples was investigated using X‐ray diffraction and Raman analyses. Diffuse reflectance spectra were obtained using a UV–Vis–NIR spectrometer and used to estimate the band gap energy. In X‐ray diffraction patterns from the synthesized compounds, the diffraction peaks were found to shift to higher 2θ values with increasing x, indicating a decrease in the lattice constants. In addition, the estimated band gap energy increased from 0.86 to 1.53 eV with increasing x. Cu2Sn1 − xGexS3 is, therefore, a potential candidate for use as the absorber layer in thin film solar cells because its band gap energy can be adjusted simply by varying its composition.

The preparation of synthetic rubber with tensile strength identical to that of natural rubber is a long-standing unsolved problem in chemistry despite extensive related research. Here, we prepare synthetic rubber with tensile strength identical to that of natural rubber as a result of our discovery that natural rubber is a naturally occurring nanocomposite with proteins and lipids. The synthetic rubber is prepared by chemically attaching nanoparticles onto microparticles of synthetic cis-1,4polyisoprene dispersed in water as a colloidal dispersion, followed by drying to form an "island-nanomatrix structure" similar to that of natural rubber. The stress at break of synthetic cis-1,4-polyisoprene increases dramatically from 0.1 to 3.9 MPa. The cis-1,4polyisoprene with an island-nanomatrix structure exhibits almost the same mechanical properties as natural rubber. In addition, the synthetic cis-1,4-polyisoprene with an island-nanomatrix structure is vulcanized in the conventional manner using sulfur, zinc oxide, a vulcanization accelerator, and stearic acid at 150 °C and 15 MPa for an optimal vulcanization time after mechanical mixing. The stress at break of the resulting vulcanized cis-1,4-polyisoprene with an island-nanomatrix structure is 35.2 MPa, which is higher than that of vulcanized natural rubber. The preparation of synthetic rubber with mechanical properties identical to those of natural rubber is achieved by the formation of an island-nanomatrix structure in the synthetic rubber and is demonstrated by the mechanical properties of the vulcanized synthetic rubber being identical to those of vulcanized natural rubber.

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