The Working Mechanism Of The Electrodes Buffer Layer In The Small Molecular Organic Solar Cells

The small molecular organic solar cell is one of the research field of organicoptoelectronic devices. Compared with the inorganic solar cells, the organicphotovoltaics （OPV） have lower production costs, convenient design/synthesis ofnew materials, simple device structure, enables flexible substrate based roll-to-rollprocess, utilizes the conventional production facilities, integrated application of theconventional organic electronic device technology, realizes transparent device. Basedon these advantages, the OPV will join in the solar cell fields to benefit our life.For the small molecular organic solar cell, an appropriate electrode buffer layercan improve the performance of the devices. In order to ameliorate the performancefurtherly, we investigate the cathode buffer layer which also can be referred to theexciton blocking layer （EBL） with CuPc and the anode buffer layer with F¹⁶CuPc.Firstly, we demonstrate the the working mechanism of organic photovoltaic（OPV） cell with CuPc as exciton blocking layer. The new exciton blocking layer（EBL） material copper phthalocyanine （CuPc）, commonly has been being used aselectron donor in the organic PV cells due to its donating-electron property andhole-transporting. But here we proved that the α-polymorph CuPc layer can transferelectrons to Al cathode through the half-filled b1g level, the mechanism of such aEBL is different from that of general EBL with larger band gap and electron-transporting property, which is based on damage states induced by heatevaporating Al.Secondly, Significant enhanced performance of organic solar cells withF¹⁶CuPc as the anode buffer layer was demonstrated. On the one hand, the adoptedF¹⁶CuPc anode buffer layer leads to the oriented growth of the CuPc molecules,resulting in the increased crystallinity and hence the hole mobility of the CuPc film.On the other hand, a dipole layer can be formed in the F¹⁶CuPc/CuPc interface,which can improve the hole extraction efficiency from CuPc to ITO. Owing to thesetow effects, the charge carriers collection efficiency was raised, while the seriesresistance and the photogenerated charge carrier recombination probability weredecreased. Consequently, the short-circuit current and the fill factor were increased.Meanwhile, the built-in potential of the devices was also increased by theintroduction of F¹⁶CuPc, leading to an increased open-circuit voltage. At the sametime, the lifetime of devices is3.3times of the refencence device.