Mechanism And Development Of Functional Small Mass Molecules To Enhance The Stability Of Perovskite Solar Cells

After just over a decade of research,the photoelectric conversion efficiency(PCE)of perovskite solar cells(PSCs)has exceeded 25%,which is close to that of commercial silicon-based cells.However,limited by the instability of perovskite materials,the practical process of PSCs is slow.Ion migration is the main reason that leads to the instability of hybrid perovskite materials and affects the working life of devices.In this paper,three kinds of small molecular materials are introduced to passivate the interface defects of perovskite and reduce the ion migration channels.At the same time,the crystal growth process of perovskite is regulated,the film quality of perovskite is improved,and the energy band structure between perovskite layer and charge transfer layer is optimized.Finally,the stability and PCE of devices are improved,the passivation mode and the influence mechanism of small molecules on the interface charge transport of devices are studied in detail.The main research contents are as follows:1.The glycine with carboxyl group and amino group was introduced to passivate the defect of interface and improve the stability of the device.In the atmosphere,glycine was added to perovskite by two-step method.Through the interaction between the carboxyl group and perovskite,slowed down the growth rate of perovskite crystal and increased the grain size to reduced the grain boundaries(GBs)and passivated the defects.The hydrophobic amino can improve the surface tension of film,effect to block erosion of water molecules in the process of perovskite crystal and enhance the moisture stability of devices.The device efficiency can reach 18%which prepared at nearly 70%relative humidity(RH)conditions,and the efficiency remained more than 80%of the initial value after exposed to 50%RH in the air for 300 h without encapsulation.2.Potassium acetate salt with carboxyl group was introduced to inhibit iodide ion migration and eliminate hysteresis of devices.The iodide ion in perovskite crystal structure is partially replaced by acetate ion,which can reduce the band gap width of perovskite material,widen the light absorption range of perovskite film and inrease the photocurrent of devices.Potassium ions can be added into the lattice gap of perovskite to passivate GBs defects,thereby inhibiting iodide ion migration and eliminating hysteresis of devices.Through the synergistic passivation of these two ions,reduced the defect density of perovskite,inhibited the carrier recombination,accelerated the hole extraction rate,which lead to the stability enhanced and the PCE improved of the devices.Finally,the device efficiency increased from 18.54%to 20.8%,and the hysteresis factor was only0.05.3.The liquid crystal molecule with cyanogroup was introduced as a"patch"to passivate the GBs defect,which improve the stability and enhance the PCE of the devices.The cyanogroup of liquid crystal molecular structure as lewis base can interact with Pb²⁺lewis acid of perovskite by hydrogen bond,which slow down the growth rate of perovskite crystal,increase the grain size,and improve the crystallization performance of film.Meanwhile,the liquid crystal molecules are filled in the perovskite GBs as"patches"to reduce the defects and ion migration channels of perovskite crystal.In addition,liquid crystal molecules can also regulate the growth orientation of perovskite crystals,which the grow direction preferentially changed from(110)to(202),lead to electron transport accelerated and charge recombination inhibited at the interface.By optimizing the preparation process of perovskite,the PCE of 20.19%was obtained.Furthemore,the perovskite film can effectively prevents the invasion of moisture because of the hydrophobic alkyl long chain.So that the devices without encapsulation placed in70%RH air for 500 h,the efficiency is still remained more than 90%of the original value.