| Although fossil energy is indispensable in our daily life,it poses a serious threat to the environment.Therefore,the study of solar photovoltaic has been widely studied by the majority of researchers.Perovskite solar cells（PSCs）have developed rapidly in the past 10 years due to the excellent characteristics of perovskite materials,such as long carrier diffusion length and low exciton binding energy,so the current power conversion efffciency（PCE）can reach certification efficiency of 25.7%at present.The rapid development of PSCs at home and abroad proves that its development will have inestimable potential and bright prospects in the future.PSCs is mainly divided into three types according to its structure,namely mesoporous,normal structure and inverted structure PSCs.Due to the high temperature sintering of mesoporous materials and the complicated process in PSCs with mesoporous structure,they are gradually abandoned.Compared with inverted structure devices,normal devices generally show higher device performance,among which the devices with Sn O2 as the electron transport layer（ETL）and Spiro-OMe TAD as the hole transport layer（HTL）structure obtain the best device performance according to the reported literature,it means that this structure has great potential as a single section PSCs.Therefore,our research object is for the devices with the normal structure in this paper.Although it has the above advantages,there are still some problems to be further optimized in this structure,such as poor quality of perovskite film and charge transport layer.At present,the preparation for the Sn O2 film usually is used commercial Sn O2 colloidal precursor,which causes the problem of uneven Sn O2 film obtained by colloidal particle agglomeration.At the same time,the defects with Sn O2 and perovskite films are easy to cause carrier non-radiative recombination reducing the performance of the device.Besides of existing the problems in the lower surface of perovskite connected to Sn O2,the upper surface of perovskite contains lead iodide（Pb I2）which is harmful to the device performance,resulting in perovskite degradation and thus effecting device stability.Finally,the migration of iodide ions（I-）in perovskite will not only cause hysteresis of the device,but also I-were migrated to Spiro-OMe TAD,which will eventually lead to the decrease of the conductivity for Spiro-OMe TAD HTL.Such a series of problems will eventually lead to the degradation of the efficiency and stability of the device.To solve the problem of perovskite film and charge transport layer,different strategies and means can be used to optimize each film,which is the easiest way to realize device optimization.However,this scheme involves many steps,and there is a risk that the optimized results of perovskite layer and charge transport layer cannot be integrated in the final device preparation.Based on reducing the complexity of the experiment and improving the performance of the device at the same time,it is a better solution to optimize the perovskite layer and charge transport layer film with the same strategy and means.This paper mainly explores the feasibility of using the same optimization strategy according to the problems existing in perovskite and charge transport layer.In this paper,the structure of perovskite solar cells based on ITO/Sn O2/Perovskite[（FAPb I3）0.93（MAPb Br3）0.07]/Spiro-OMe TAD/Ag were studied.For the Sn O2 ETL and perovskite bilayer films（defined as Sn O2/Perovskite）as well as the Perovskite and Spiro-OMe TAD HTL bilayer films（defined as Perovskite/Spiro-OMe TAD）interfaces,the Sn O2 ETL and perovskite films were optimized by doping modification of ammonium citrate（TAC）,and the perovskite films and Spiro-OMe TAD HTL were optimized by precursor（Cs-I）containing Cs and I ion treatment,respectively.Finally,the device efficiency and stability were improved.The data analysis and characterization of the perovskite and the transport layer are carried out in combination with the testing methods of the film,and the following two conclusions were finally obtained:1.Firstly,the doping modification strategy was adopted in this paper.The Sn O2/Perovskite bilayer film was optimized by using small molecule ammonium citrate（TAC）as the dopant of Sn O2,including better conductivity of Sn O2,reduction of oxygen vacancy defects of Sn O2 and uncoordinated lead ion defects of perovskite,and better film crystal quality.The performance of PSCs can be improved by doping an effective and simple multifunctional TAC into Sn O2 precursor.Sn O2 dopped TAC can obtain more evenly distributed Sn O2 colloidal particles,and improve the conductivity of Sn O2 film.The interaction of TAC functional groups between perovskite and Sn O2 effectively have passivated interface defects including oxygen vacancy in Sn O2 film and uncoordinated Pb2+in perovskite film.By constructing perovskite nucleation sites on the surface of Sn O2,grains of the large size and vertically grown across the cross section can be induced to form for improving the quality of perovskite films.Besides,the better energy level arrangement is obtained in Sn O2/Perovskite.And the hysteresis of the device was reduced through the combination of N-H…I forming hydrogen bonds.The results show that the PCE of TAC-doped Sn O2 ETL devices increases from 19.75%of control devices to21.58%.Finally,the stability of the device is also signiffcantly improved;the unencapsulated device with TAC modiffcation retains 88%of its initial PCE after storing for about 1000 h under dark and 10-25%RH conditions.The work emphasizes the importance of using small molecules as additives to obtain better electrical conductivity of Sn O2 films and improve the quality of perovskite crystals to achieve the optimization of dual films.This study provides an important technique for further improving device performance through doping modification strategy to better understand that the improvement of device performance is closely related to the quality of Sn O2 film and perovskite film2.Except SnO2/perovskite bilayer films properties is very important for device performance,as a whole in the device,Perovskite/Spiro-OMe TAD bilayer films are also critical to device performance.Therefore,for the Perovskite/Spiro-OMe TAD bilayer film,we adopted simple and effective interface engineering strategy to optimize Perovskite/Spiro-OMe TAD bilayer film by modification with synthetic Cs-I precursor（iodine is mixed with cesium acetate）,which include reduction of perovskite interface and bulk phase defects and improvement of Spiro-OMe TAD conductivity.Firstly,Cs-I reacts with lead iodide（Pb I2）which deteriorates device performance to reduce the uncoordinated lead ion(Pb2+)defects and finally form theδ-Cs Pb I3 which is more hydrophobic and relatively more stable at room temperature,thus turning the waste of Pb I2,which is harmful to device performance,into treasure.Simultaneously,Cs-I-modified perovskite films quality was improved,mainly attributing to the small volume of Cs+entering the perovskite to stabilize the lattice of that.In addition,since theδ-Cs Pb I3formed exists on the surface of perovskite,more matching energy level between Perovskite/Spiro-OMe TAD is obtained,which is conducive to charge transport.At the same time,it was found that iodine signals were not detected on the surface of Spiro-OMe TAD after Cs-I-Modified treatment,which was mainly due to Cs+entering the perovskite to stabilize the lattice of that,and iodine inons could fill defects of iodide vacancies.Thus,migration of I-towards to the surface of Spiro-OMe TAD were reduced,which is beneficial to reduce the risk of Spiro-OMe TAD conductivity deterioration and continued degradation of perovskite due to the reaction of iodide ions with silver electrodes.Finally,the PCE of the PSCs based on Cs-I-Modified was increased from19.62%of control device to 21.21%.Under the dark and 15%-25%RH conditions,the device performance with Cs-I-Modified can still maintain about 80%of its initial PCE after 1200 h,showing excellent improvement of device performance for efficiency and stability.This study provides an important technique for further improving device performance through interface engineering strategy to better understand that the improvement of device performance is closely related to the quality of Spiro-OMe TAD film and perovskite film... |
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