Metal Electrode-free Perovskite Solar Cells Based On Carbon Nanofibers

Perovskite solar cell is a new type of solar cell with the most rapid development in recent years.Since its appearance,the research of improving the photoelectric conversion efficiency（PCE）of perovskite solar cells has attracted the attention of researchers.At present,its PCE has increased from 3.8%to 25.5%.Adding metal ion salt to the inorganic electron transport layer is one of the effective methods to improve the PCE of perovskite solar cells.After improving the PCE,it is necessary to further improve the stability of its exposure to the external environment.Precious metals such as gold and silver are often used in the electrode of perovskite solar cells.Precious metal electrodes are expensive and the preparation process is complicated.Moreover,the metal electrode reacts slowly with the perovskite layer,which affects the stability of the battery.Therefore,it is necessary to develop a low-cost and stable back electrode to replace the traditional metal back electrode,which is one of the most important work to realize the commercialization of perovskite solar cells.In this paper,we first discuss the different concentrations of sodium chloride（NaCl）doped tin oxide（SnO₂）electronic transport layer to improve the performance of perovskite solar cells.Then we use the electrostatic spinning technology and coking technology to prepare carbon nanofibers.Finally,we use the obtained carbon nanofibers to make metal electrode-free perovskite solar cells in different ways.Main contents of the paper:（1）Modification and preparation of SnO₂-based perovskite solar cells:NaCl was doped into SnO₂ solution,and the effect of different NaCl doping concentration on SnO₂ electron transport layer and perovskite layer was studied.UV-vis spectrophotometer（UV-Vis）,Field emission scanning electron microscopy（FE-SEM）,X-ray photoelectron spectroscopy（XPS）were used to observe the SnO₂ and perovskite films.The results showed that the surface morphology of SnO₂thin films was the best when the mass fraction of NaCl was 2wt%.The perovskite thin films prepared on this concentration doped SnO₂ thin films had compact structure,large crystal particles,and the performance test of the assembled devices was the best.Moreover,due to the migration of the metal Na⁺,the hysteresis,which is common in SnO₂-based perovskite solar cells,was also eliminated.（2）Preparation of metal electrode-free perovskite solar cell by laminated method:This experiment explored the effects of different applied voltages and polymer solution extrusion rates on the morphology of electrospinning PAN nanofibers.And the effects of different carbonization temperatures on the morphology and properties of carbon nanofibers were explored.Field emission scanning electron microscope（FE-SEM）,video contact angle measuring instrument and four-probe resistance measuring instrument were used to observe the prepared nanofibers.The results showed that when the applied voltage was 20k V and the polymer extrusion rate was0.009ml/min,the obtained PAN nanofibers had the best morphology.Then,the PAN nanofibers obtained by this parameter were calcined at different carbonization temperatures,and the obtained carbon nanofibers were used to prepare metal electrode-free perovskite solar cells.It was found that the higher the temperature,the better the electrical conductivity of the carbon nanofibers.The PCE of the metal electrode-free perovskite solar cell prepared at the carbonization temperature of1200℃was 2.1%.（3）Preparation of metal electrode-free perovskite solar cell by scratch-coating method:When using laminated method to prepare metal electrode-free perovskite solar cell,the combination between carbon nanofibers and perovskite functional layer was poor,and it was easy to fall off,resulting in low filling factor and low PCE of the devices.In order to improve the PCE of the device,carbon nanofibers were ground up and mixed with adhesive to prepare carbon paste.Then the carbon slurry was used to construct metal electrode-free devices.Compared with the metal electrode-free device prepared by laminated method,the metal electrode-free device based on carbon paste showed higher PCE.The resulting carbon nanofiber film could better combine with the perovskite functional layer.The filling factor of the device obtained was higher,and the PCE of the device was increased to 4.87%.