Research On Carbazole Photosensitizers In Dye-sensitized Solar Cells

Dye-sensitized solar cells（DSSCs）as the third generation solar cells with excellent performance have been widely studied and applied.Photosensitizers play an important role in DSSCs,which affect the photovoltaic performance of the device.A series of new organic photosensitizers were designed and synthesized in this paper.The photoelectric properties of these dyes have been systematically studied.Using 2-trifluoromethylbenzoic acid and 3-trifluoromethylbenzoic acid as the acceptor groups,two new D-A-π-A organic photosensitizers were synthesized,namely SL201 and SL202.From the UV-vis absorption spectrum,it can be seen that SL dyes have wide absorption spectrum and large molar absorption coefficient.The trifluoromethyl as strong electron-withdrawing group was introduced to benzoic acid acceptor.Due to the influence of steric hindrance,it leads to the molecular planarity of SL201 and SL202 are different.The molecular planarity of SL202 is better than SL201,which makes the intermolecular conjugation of SL202 is better and the UV-vis absorption spectrum of SL202 be broadened.Due to wider spectral response range and more the dye-load amount of SL202 on the TiO₂film,using the[Co（bpy）₃]^2+/3+liquid electrolyte,the device based on SL202 had achieved the power conversion efficiency（PCE）of 9.8%.Under the same conditions,the device based on SL201 showed the PCE of 9.0%,but it had a higher open circuit voltage(V_oc)of 927 m V.The photosensitizer SL201 had a large torsion angle,which affects its arrangement on the TiO₂film,thereby can effectively inhibit the electron recombination between the device interfaces and obtain a higher V_oc.Based on triazatruxene（TAT）,using rigid groups of ten aromatic ring（BTC）as donor,thiophene asπbridge,benzothiadiazole as a additional acceptor and dipicolinic acid as acceptor,organic photosensitizer was designed and synthesize,namely SL301.The photosensitizer SL301 had a narrow UV-vis absorption range,which affect the photoelectric performance of the device.In order to broaden the absorption spectrum and improve the photoelectric performance of the device,the blue photosensitizer SL302 was synthesized.The photosensitizer SL302 was designed with indolo[3,2-b]carbazole as the donor,thienopyrrolidone as theπbridge,and benzoic acid as the anchor group.The UV-vis absorption spectrum of SL302 is wider than the photosensitizer SL301.In this paper,the photosensitizers SL302 and SL301 were mixed at different concentrations for co-sensitization,with using Co²⁺/Co³⁺as the liquid electrolyte,exploring the effect of co-sensitization on the photoelectric performance of the device.Finally,the devices based on SL301 achieved the PCE of 5.28%,based on SL302 achieved the PCE of 6.32%,while based on co-sensitization got a PCE of 7.12%.By co-sensitization,the absorption spectrum was broadened and the response value of the IPCE curve more larger and its range more wider.