Polymer-based Solar Cell In Tandem Structure

Solar cells based on organic and polymer materials have the potential advantages of low cost and light weight compared with traditional solar cells. However, organic solar cells have not yet reached the level of practical use due to their lower efficiency compared to, e.g., silicon-based devices. One possible way to improve the efficiency is by using a tandem configuration in which two or more cells with different absorption spectra, i.e., different band gaps, are stacked. This increases the absorption of solar light and allows utilizing the photon energy more efficiently. In a two terminal tandem cell, with the active layers connected in series, the open-circuit voltage( Voc)is the sum of the Voc's of the subcells. In order to construct an organic or polymer tandem solar.The influence of the thickness of organic thin films to the solar cell is studied in this paper through MEH-PPV/C₆₀ bulk heterojunction devices. It is concluded that with the increase of the thickness of the organic thin film, the short current decreased. This is because the diffusion length of the carrier is limited, the increase of the thin film thickness reduces the possibility that the carriers reach the electrod, and increases the possibility that the carriers compound. Therefore, it is limited to enhance the performance of organic solar cell by changing the thickness of organic thin films.In order to construct an organic or polymer tandem solar cell, a transparent intermediate layer positioned between the two active layers is required, which provides electrical contact between the two cells via efficient recombination of the holes and electrons created in the different subcells without voltage loss. In this letter, we present a straightforward and versatile solution-based method to process electron and hole transport layers consisting of TiO₂ nanoparticles and poly₃,4-ethylenedioxythiophene_<sub><sub>PEDOT_, respectively.The TiO₂ layer is deposited by means of solgel chemistry. The TiO₂ layer serves three separate functions. First, hydrophilic TiO₂ separates the PEDOT:PSS that is cast on it from aqueous solution, from the underlying hydrophobic MEH-PPV/C60 charge-separating layer of the front cell; the hydrophobic TiO₂ precursor becomes hydrophilic after conversion to TiO₂. Second, the TiO₂ layer breaks the symmetry in the front cell and thereby creates the open-circuit voltage. Third, the TiO₂ functions as an electron transport layer. Fourth, the TiO₂ functions as a hole blocking layer because the top of the valence band of TiO₂ is sufficiently electronegative, 8.1 eV below the vacuum, to block holes.Finally, we make two tandem solar cell and find that the Voc is improved .