Improving The Performance Of Inverted Perovskite Solar Cells By Optimizing Hole Transport Materials And Perovskite Film Modification

Organic-inorganic hybrid perovskite materials have attracted wide attention due to their excellent photoelectric properties such as ideal and adjustable band gap,strong optical absorption,long carrier diffusion length,decent carrier mobility,low exciton binding energy and balanced bipolar carrier transport.Over the past ten years,photoelectric conversion efficiency（PCE）of perovskite solar cells（PSCs）has dramatically increased from 3.8%to 25.5%.However,at present,high-efficiency PSCs are mostly based on the conventional（n-i-p）structure,and the fabrication of the electron transport layer in high-efficiency PSCs usually requires a high-temperature sintering process at 500°C,which greatly increases the cost of device preparation.On the other hand,the hole transport layer（HTL）used in n-i-p devices generally needs to be doped to increase its hole mobility.The instability of the devices caused by HTL doping coupled with the high price of the expensive hole transport materials further hinder its commercialization process.Inverted PSCs possess advantages including facile fabrication,low-temperature processability,negligible hysteresis,and potential for large-scale production and flexible applications,rendering them competitive in future commercialization.However,the efficiency of p-i-n structure perovskite solar cells is much lower than that of the devices based on n-i-p structure.The low open circuit voltage(V_oc)is the main reason for inferior efficiency of inverted PSCs.The main factors affecting V_oc is interface energy loss between perovskite and HTL.well-matched energy levels between HTLs and perovskite materials is effective increase the V_oc of the device.On the other hand,due to the solution-based manufacturing process and the ionic nature of the perovskite material,there are still some defects in the perovskite film.These defects could act as non-radiative recombination centers and thus deteriorate the performance of PSCs.At the same time,due to the chemical degradation of the perovskite material caused by defects,the long-term stability of PSCs is also adversely affected.It is recognized that the reduced defects and contact passivation of perovskite film is critical to obtain photovoltaic device with excellent performance.Therefore,it is potential to improve the quality of perovskite film by additive engineering.This paper focuses on adjusting the photoelectric properties of P3CT hole transport materials and improving the quality of perovskite films through additive engineering to achieve efficient and stable inverted perovskite solar cells.The researches content are summarized based on the following three chapters:1.Poly[3-（4-carboxybutyl）thiophene-2,5-diyl]（P3CT）has been noticed as a promising hole transport layer for high-performance inverted planar perovskite solar cells due to its excellent stability and relatively high hole mobility.In this work,P3CT is used to react with alkali metal ions Na⁺,K⁺,Rb⁺,Cs⁺to synthesize P3CT-Na,P3CT-K,P3CT-Rb,P3CT-Cs HTL,respectively,and we fabricated inverted perovskite solar cells based with different hole transport materials.It turned out that the addition of Rb⁺ions appropriately reduced the degree of molecular aggregation of the P3CT,and increased the work function of P3CT-Rb so that it had a well-matched valence band with the perovskite layer.At the same time,the hole mobility of P3CT-Rb HTL has been further improved.On the other hand,perovskite(MAPb I_3-xCl_x)film deposited on top of the P3CT-Rb film exhibited a dense and uniform morphology with superior crystallinity and few pinholes.Consequently,a high efficiency of 20.52%was achieved on P3CT-Rb HTL-based devices,with an impressive V_oc of 1.144 V and a high fill factor（FF）of 82.78%.2.Diprophylline is first used to modify the P3CT-Na HTL in inverted PSCs.Diprophylline modifies work function of ITO（indium tin oxide）by self-assembling onto the ITO surface.Meanwhile,it could interact with P3CT-Na through hydrogen bonding interaction,thus inducing ordered arrangement of P3CT-Na molecules,and increasing transmittance of the HTL.In addition,diprophylline could partially dissolve into the upper perovskite layer,and facilitate the perovskite crystallization.As a result,inverted PSCs utilizing diprophylline added P3CT-Na as HTL yield a remarkable efficiency of20.87%and excellent long-term stability.Notably,the FF is approaching 84%,representing one of the highest results in inverted PSCs.More interestingly,when the diprophylline treated P3CT-Na layer undergoes ultrasonic cleaning in deionized water for10 mins,the as-fabricated PSCs still show a high efficiency of 18.77%,manifesting good durability of the HTL.Thus,the recyclability and cost-effectiveness of the HTL makes it more applicable in future commercialization.3.High-quality perovskite film is critical to realize efficient photovoltaic performances of perovskite solar cells（PSCs）.In order to reduce the trap density and passivate non-radiative recombination centers of perovskite film,scandium trifluoromethanesulfonate（Sc（OTF）₃）is introduced into the perovskite precursor solution as a multifunctional additive.The sulfonic group could coordinate with lead ions,thus reducing the perovskite crystallization process,and high-quality perovskite film with large grain size,high crystallinity and few defects is obtained.Meanwhile,the doping of rare earth ion Sc³⁺in perovskite precursor solution could interact with perovskite,thereby improving film morphology and prolonging the charge carrier.In addition,the strong hydrogen bonding interaction between Sc（OTF）₃ and MA⁺could immobilize methylamine ion（MA⁺）,contributing to the improved stability of perovskite film.As a result,inverted PSCs with Sc（OTF）₃ in a low doping amount of 0.1 mg/m L shows a remarkable efficiency of 20.63%along with V_oc of 1.134 V,a short circuit current density(J_sc)of 21.71 m A/cm²,and a high FF of 83.80%.