| Organic solar cells (OSCs) has the advantages of being thin and light weight, flexible and rollable, rich in raw materials as well as be easily fabricated in large area through roll-to-roll manufacturing. OSCs are considered as typical representatives of new clean energy. Compared with conventional silicon cells, the conversion efficiency of OSCs is still low and so is their stability, besides, some in-depth exploration of mechanism issues in OSCs are still needed.OSCs are devices than can transfer solar energy into electrical energy. The performance of OSCs is decided by open circuit voltage (Voc), short circuit current density (Jsc), fill factor (FF). Actually, the performance of OSCs are generally easy affected by many factors, such as types and purity of the materials, film morphology, ambience of moisture and oxygen, illumination as well as temperature. Meantime, temperature is one of the most common factors that have great influence on the performance of organic electronic devices. The generation of photocurrent in organic solar cells is a relative complicated process, which can be divided into the following four basic processes:light absorption and excitons generation, exciton diffusion, exciton dissociation, free charge transport and collection. Each of these five processes can be affected by temperature. Therefore it is necessary to research the temperature-dependent properties of OSCs to deepen our understanding and enhance the performance of OSCs. Our effort focused on two parts:(1) Investigation on the temperature dependent-photocurrent in CuPc/C6o based OSCsAccurate measurement and control of temperature in the range of 77-300 K were realized using a probe station. Combined with an optical system built up by myself, the absorption spectra of CuPc film at low temperatures was gained for the first time. Little change of absorbance at different temperatures was found in the wavelength range of 530-800 nm. So the exciton generation and absorption efficiency showed little change with different temperatures. However, the external quantum efficiency (EQE) from 77 to 300 K of the developed device shows monotonically increasing with raising temperatures and the average growth rate is 0.12 %/K. Through a detailed analysis of the EQE affecting factors, we believe that the increase of photocurrent in the device is mainly due to the increase in exciton diffusion and dissociation efficiency with temperature, rather than the increase of mobility as reported in other literatures.(2) Investigation on the temperature dependent-photocurrent in Pentacene/C6o based OSCsPentacene is a better spectral matching donor material than CuPc, and unlike other materials, for example, CuPc, there are singlet fission in pentacene. Singlet fission a non-adiabatic process in which one singlet excited state splits into two triplets that ultimately give rise to four charge carriers, which has significant importance for improving the performance of OSCs. Using the same system, we investigated the absorption spectra of pentacene on film thickness and temperature as well as the J-V characteristics, EQE of pentacene/C6o based OSCs at different temperatures. Obvious increase of EQE with temperature was observed, but the EQE increase at different wavelength varies a lot. At 660 nm, the increase of EQE is about 20%, which is the minimum increase. It is believed the variation of EQE at different wavelengths is a result of the unique exciton process in pentacene. |
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