engleski

Small molecule photoabsorbers for application in photovoltaic devices

Recently, organic photovoltaic devices have received increased attention due to combination of their comparatively simple and cost effective processing and ability to derive low weight, flexible thin-film solar cells. The process of electron-hole pair generation and its extraction toward the electrodes is essential to achieve high performance for all photovoltaic devices and can be influenced by a number of common approaches, such as tuning the bandgap of the photoactive material i.e. broadening the HOMO/LUMO levels (deepening the HOMO levels of the donor material), as well as optimization of the deposition geometry i.e. tailoring the optimal film morphology through molecular interactions to achieve high charge carrier transfer. The latest is of particular interest for small photoactive organic molecules, such as squaraine (SQ) dyes and their derivatives, as they show great preference in supramolecular assembly based on molecular design when deposited into thin-films [1]. SQ photoactive layers (donor materials) used in solar cells are generally mixed with acceptor materials, such as fullerene or their derivatives (e.g. PCBM) into bulk heterojunction layers such approach may widen the absorption spectra [2]. In this study, an optimal synthesis route and film deposition parameters were determined by mixing of several SQ based materials with a number of commercial acceptor materials in various ratios and subsequent depositions. The samples were characterized through SEM and AFM to examine film morphology and UV/Vis spectroscopy to determine the absorption spectra. Furthermore, GIXRD measurements revealed the crystalline constituent layers of the prepared cells and suggested possible presence of any superstructural organisation. We correlated the nature and number of substituents linked onto the SQ base to some degree of functional performance of the synthesized films and thereof assembled photovoltaic devices.

Organic solar cells, electron transport, thin films

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