Inverted Planar Perovskite Solar Cells Based On Modified PEDOT:PSS With High Efficiency And Stability

Organic-inorganic hybrid perovskite solar cells(PSCs)have attracted widespread attention since their first demonstration in 2009 because of their outstanding optoelectronic properties and lower production costs.The power conversion efficiency of PSCs has been promoted from 3%to 25.5%over the past decade,and the stability under light conditions and more than 1,000 hours which make it show great promise for deployment as the next generation of photovoltaics.The structure of perovskite solar cell can be divided into planar structure(n-i-p)and inverted planar structure(p-i-n).Inverted planar PSCs have attracted widespread attention in the photovoltaic field due to their better air and humidity stability,smaller hysteresis and better photovoltaic integration possibilities,which has initiated a research boom to improve the efficiency of inverted planar perovskite solar cells.The rapid enhancement has partly benefited from the employment of suitable hole transport layers.Especially,the p-type PEDOT:PSS is widely utilized as the hole transport layer(HTL)for solution-processed PSCs with a p-i-n structure,because of its high optical transparency in the visible region and low-temperature processing condition.However,the inverted PSCs based on PEDOT:PSS HTL suffer from deficient open-circuit voltage(V_OC)and poor stability issues,because of the high electron affinity and acid nature of PEDOT:PSS,which severely restricts the commercialization of IPSCs.Therefore,this thesis focuses on the problems of low work function,strong hydrophilicity and low conductivity of PEDOT:PSS,and uses two methods of interface modification and doping modification to modify PEDOT:PSS,so as to obtain high efficiency and high stability inverted planar perovskite solar cells.The main research contents and results are as follows:(1)Perovskite solar cell based on sodium hydroxide(NaOH)modified PEDOT:PSS film.The PSCs using FA_0.2MA_0.8PbI_3-xCl_x as the perovskite light-absorbing layer and NaOH modified PEDOT:PSS as the hole transport layer.The study found that NaOH neutralized the PSS group of PEDOT:PSS,and the H⁺on PSS was replaced by Na⁺,which reduced the acidity of PEDOT:PSS and passivated defects at the interface between the perovskite and the hole transport layer.And NaOH increase the work function of the PEDOT:PSS film,and better energy level arrangement between PEDOT:PSS and perovskite.In addition,the NaOH-PEDOT:PSS layer with improved hydrophobicity and polar agent wettability to obtain a higher quality perovskite film.The V_OC of NaOH modified PSCs the increased from 1.02 V to 1.09 V,and the PCE increased from 16.75%to 18.05%.After NaOH modification,the hysteresis effect of the device was reduced.After storing for 10 days under an environmental condition of 25°C and 30-40%humidity,the efficiency only drops by 10%.This study shows that NaOH can be used to modify PEDOT:PSS to improve the performance of the device,but the strong alkalinity of sodium hydroxide and the neutralization process may affect the charge transport characteristics of the device,so it is necessary to find a weakly basic salt to modify PEDOT:PSS.(2)Perovskite solar cell based on sodium benzene sulfonate(C₆H₅SO₃Na)(SBS)doped PEDOT:PSS film.The PSCs using FA_0.2MA_0.8PbI_3-xCl_x as the perovskite light-absorbing layer and NaOH modified PEDOT:PSS as the hole transport layer.The study found that after sodium benzenesulfonate doped PEDOT:PSS,the sulfonic acid group(-SO₃H)on PSS was converted to sodium salt(-SO₃Na),which neutralized the acidity of PEDOT:PSS to prevent ITO corrosion and perovskite degradation.In addition,the SBS–PEDOT:PSS layer with improved hole extraction capacity and suppressed charge recombination,significantly increases the grain size and crystallinity of the MA_0.8FA_0.2PbI_3-xCl_x perovskite film.Consequently,the PCE and V_OC of the inverted PSCs are improved from 18.07%and 1.04 V to 19.41%and 1.08 V,respectively,after SBS modification.Moreover,the efficiency of the unencapsulated PSCs based on SBS–PEDOT:PSS remains above 90%after storing in ambient condition for 20 days.In summary,this thesis starts from the modification of PEDOT:PSS,and proposes two new technologies for interface modification and doping modification.In this thesis,a new technology for the interface modification of sodium hydroxide has been developed,and a new method for improving the performance of solar cells with sodium benzenesulfonate doped PEDOT:PSS has been discovered.This research provides a feasible way to improve the performance of planar trans perovskite solar cells.