Low Temperature Preparation Of Planar Perovskite Solar Cells

As a new-generation solar cell,perovskite solar cells（PSCs）have shown great potential development and become one of the most popular research fields.Normally,PSCs belong to a type of thin film cells,which has a structure similar to a sandwich.Different functional layers are stacked on each other to finally form a device to function.Due to its simple structure,the planar structured devices have attracted more and more attention.However,the commercialization of the PSCs is still facing great challenges,mainly due to the poor stability.Compared to the rigid devices based on the glass substrate,the flexible devices based on the plastic substrate show more advanteges such as thin thickness,light weight and flexibility.The flexible PSCs might have more chance to enter market at the current stage as they can be applied in the wearable electronics.Such an application would not require a very long lifetime.Among these functional layers,tin oxide（SnO₂）is a popular electron transport layer（ETL）,and mixed cation lead halide（CsFAMA）is currently the most promising perovskite light absorbing layer,with the power conversion efficiency（PCE）over 24%.However,the preparation process of SnO₂ and CsFAMA usually requires an annealing process to assist in crystallization,removal of impurities and solvents,etc.The annealing process greatly limits the PSCs substrate selection,which have to choose bulky,fragile but high temperature resistant conductive glass as substrate.Rigid substrate is extremely inconvenient in logistics and installation,and has high broken rate.Besides,annealing process requires strict temperature control process,annealing time must be precisely controlled as well,and the process is cumbersome.A large amount of energy is wasted and the production cost is increased during annealing process.Based on this,this paper attempts to improve the existing process in order to achieve high-performance PSCs without annealing,mainly from the following three aspects:1.Developed a room temperature hydrolysis synthesis process for SnO₂.The kinetics of the hydrolysis reaction was adjusted by the acidic environment of the SnCl₄aqueous solution to prepare SnO₂ nanoparticles（NPs）at room temperature.At the same time,through the appropriate surface treatment and optimization of the synthesis process,the goal of preparing the SnO2 ETL without annealing was achieved.The SnO2ETL prepared by the room temperature process showed a good conductivity and high efficiency of charge extration,and the PCE of the PSCs device exceeded 19%.2.Developed a room temperature synthesis process for the perovskite film.On the basis of the preparation of SnO₂ ETL at room temperature,the ratio of Cs cation of mixed cation perovskites was adjusted,and the selection of auxiliary solvents was optimized to achieve the purpose of preparing perovskite light absorbing layer at room temperature.Perovskite film can be naturally dried at room temperature by anti-solvent-assisted spin-coating.There was no need for difficult-to-regulate anti-solvent soaking or complex vacuum equipment to remove solvent.The perovskite prepared by the room temperature process can obtain 16.51%PCE on the rigid substrate,with good crystallinity,conductivity,and long charge carrier lifetime.3.Synthesized the flexible PSCs on room temperature.The flexible PSCs were prepared at room temperature with the both SnO₂ ETL and perovskite light absorbing layer process used in former two chapters.The PCBM was used to modify the interface between ETL and perovskite to eliminate the hysteresis.Reverse scan of PCE achieves14.98%,and the forward scan PCE is 14.61%;PCBM modified device even exhibited better stability.In the entire preparation process,there was simple,annealing-free process,no complicated and difficult to control process equipment invovled.In this work,by synthesizing SnO₂ NPs at room temperature and regulating the formulation of perovskite precursor solution,the process of preparing PSCs without annealing was explored with existing process,the energy consumption in the production process was reduced,the production process was simplified,and the prospect of commercialization of PSCs was greatly improved.The potential application field of PSCs was broadened,miniaturization and home furnishing for PSCs became possible.