The Study On Optimization Of Tin Dioxide Charge Capture And Transport Performance In Perovskite Solar Cells

Organic-inorganic hybrid ABX₃ perovskite materials have injected new vitality into the development of solar cells.In just a few years,the efficiency of devices based on perovskite materials has risen to more than 25%.The rapidly increasing efficiency of perovskite solar cells is inseparable from the sandwich structure of the device,under which the effective separation and collection of photo-generated carriers can be achieved.The electron transport layer is an important layer in the device structure.Compared with the traditional Ti O₂ transport layer,the SnO₂ transport layer is slightly better in conductivity,light transmittance,and stability,so it has received extensive attention and applications.However,many researchers have neglected that SnO₂nanocrystalline films will form oxygen adsorption（O₂^-）interface defect states under annealing conditions.At this time,the surface band energy of SnO₂ will be bent and the surface resistance will increase.A charge transport barrier is formed at the interface between the perovskite and SnO₂,which is detrimental to the improvement of device efficiency.On the other hand,although the electron mobility of SnO₂ crystals is high,the electron mobility between SnO₂ nanocrystalline grains is low,which also affects the charge transfer efficiency inside the SnO₂ film.In response to the above problems,the work in this paper is dedicated to improving the charge extraction and transfer performance of SnO₂,mainly including the following research:1.Optimize the efficiency of SnO₂ based devices.Under the condition of SnO₂ as the electron transport layer,by comparing the device efficiency of the light-absorbing layer CH₃NH₃Pb I₃ and CH₃NH₃Pb I_3-xCl_x,we found that the short-circuit current of the CH₃NH₃Pb I₃device is higher,but the overall performance of the CH₃NH₃Pb I_3-xCl_xdevice is better.The reason is that after chlorine doping,the band gap of the perovskite increased,so the open circuit voltage of the device has a larger gain.Therefore,CH₃NH₃Pb I_3-xClx is selected as the light-absorbing layer.Then we compared the suitability of the conductive electrode FTO and ITO with SnO₂.Since the light transmittance and flatness of the FTO film are not as good as ITO,ITO is selected as the conductive electrode.2.The interface modified SnO₂ film with guanidine hydrochloride uses the charge coupling effect of guanidine ion（GA⁺）and O₂^-defect state to weaken the interface charge transport barrier and improve the efficiency of charge extraction.XPS and FTIR test results confirmed the existence of adsorbed oxygen on the surface of SnO₂ and the charge coupling effect between GA⁺and O₂^-.After the introduction of GA⁺,the conduction band energy level of the SnO₂ film shifts down and the driving force of photogenerated electron transmission is enhanced,the device efficiency is increased from 15.33%to 18.46%,and the fill factor of the device is increased to more than 80%.Thanks to the hydrogen bonding between the amino group in the interface GA⁺and the iodide ion in the perovskite,the modified SnO₂ film improves the wettability of the perovskite,while inhibiting the formation of iodine vacancies,and the device stability is also improved.3.Green,stable and high-conductivity imidazole bromide doped with SnO₂hydrosol can improve the dispersion stability and conductivity of colloidal particles.Dynamic light scattering（DLS）characterization results show that after 1 mg/ml imidazole bromide salt is doped,the particle size distribution of the mixed hydrosol is more uniform,and the anti-coagulation property is enhanced.The morphology of the SnO₂film is flat and uniform.However,doping at a high concentration of 5 mg/ml directly caused colloidal coagulation.After spin coating,mottling appears on the SnO₂film.The J-V curve of the ITO/SnO₂-imidazole bromide/Ag structure and the steady-state PL test of the ITO/SnO₂-imidazole bromide/PVS structure show that the conductivity and charge transport ability of the doped film is enhanced.The efficiency of the device has increased from 15.50%to 17.64%,and the short-circuit current has increased by nearly 1m A cm^-2.Compared with the device without an electron transport layer,the imidazole bromide salt alone as the electron transport layer increases the short-circuit current of the device by nearly 1.5 m A cm^-2.However,due to the small molecular nature of the imidazole bromide salt,its film-forming properties are poor and the device efficiency is poor in repeatability.