Research On Efficient Charge Transport Layers For Perovskite Solar Cells

Due to the excellent photoelectric properties and simple solution preparation process of organic-inorganic hybrid perovskite materials,organic-inorganic hybrid perovskite solar cells have developed rapidly in just seven or eight years.At present,its power conversion efficiency is comparable to that of commercial silicon-based solar cell.However,many problems such as serious hysteresis,long-term instability and cost of raw materials in devices also limit their large-scale commercial applications,which need to be solved urgently.In order to solve the problems above,this paper takes high-efficiency and stable perovskite solar cells as the research objective,and takes charge transport layer materials as the starting point and main research content,systematically studies and explores the effects of novel electron transport layer,hole transport layer and modification of charge transport layer on the performance of perovskite solar cells.The main research contents and conclusions are summarized as follows:(1)In this work,we regulated the electron transport ability by doping Zn O with Mg,and then employed the optimized Mg-doped Zn O/PCBM as the composite electron transort layers(ETLs)of planar devices for the first time.Due to the improved carrier injection/transfer and subsequently enhanced photo-current and voltage in the devices with Mg-doped Zn O,a significant improvement in PCE,from 13.86% with the pristine Zn O ETL to 16.74% with the optimized 2% Mg-doped,has been achieved.Meanwhile,a higher power conversion efficiency(PCE)of 17.85% through a PCBM interfacial layer between the 2% Mg-doped Zn O and perovksite layer has been achieved.More significantly,the devices with 2% Mg-doped Zn O/PCBM composite ETLs also demonstrate outstanding long term device stability and up to 91% of original efficiency of the PKSCs,which can be retained even after exposure in ambient conditions over three-months.(2)Herein,we manifest that low-temperature solution-processed Zn Se can be used as a potential ETL for perovskite soalr cells(PKSCs).Our optimized device with Zn Se ETL has achieved high PCE of 17.78 % with negligible hysteresis,compared with theTi O2 based cell(13.76%).This enhanced photovoltaic performance is attributed the suitable band alignment,high electron mobility and reduced charge accumulation at the interface of ETL/perovskite.Encouraging results were obtained when the thin layer of Zn Se cooperated with Ti O2.It shows that the device based on the Ti O2/Zn Se ETL with cascade conduction band level can effectively reduce the interfacial charge recombination and promote carrier transfer with the champion PCE of 18.57%.In addition,the Zn Se-based device exhibits a better photostability than the control device due to the greater ultraviolet(UV)light-harvesting of the Zn Se layer,which can efficiently prevent the perovskite film from intense UV light exposure to avoid associated degradation.Consequently,our results present that a promising ETL can be a potential candidate of the n-type ETL for commercialization of efficient and photostable PKSCs.(3)In this work,we firstly improve the electron transport properties by modification of Ti O2 ETL with Na species,and an enhanced PCE of 16.91% has been obtained with less hysteresis.Subsequently,inorganic Cu I film prepared by a facile spray deposition method has been employed to replace the conventional spiro-OMe TAD as the hole transport layer(HTL)in PKSCs.Due to the improved transport properties at the ETL/perovskite and perovskite/HTL interfaces,a maximum PCE of 17.6% with reduced hysteresis has been achieved in the device with both the Na-modified Ti O2 ETL and 60nm-thick Cu I layer HTL.To our knowledge,the PCE achieved in this paper is one of the highest values ever reported for the devices with inorganic HTLs.More significantly,the devices manifest an outstanding device stability,the PCE keeps constant after storage in the dark for 50 days,and it can retain approximately 92% of their initial efficiency after storage even for 90 days.(4)We have exhibited a novel,green,and eco-friendly Mn S film via the technique of vacuum vapor deposition without any solution and annealing process that can be used as a potential HTL in PKSC.As a result,the optimized device based on Mn S has achieved high PCE of 19.86% with negligible hysteresis,which is comparable with the Spiro-OMe TAD based cell.To our knowledge,the PCE achieved in this paper is one of the highest values ever reported for the PKSC devices with inorganic HTLs.Besides,Mn S based PKSC has retained over 90% of their initial efficiency after stored in approximately 80% humidityenvironment for 1000 h without encapsulation.More importantly,it also has shown superior long term stability under harsh condition(85 °C,?80% humidity,1-sun)retaining80% of the initial efficiency after 400 h.These results highlight its great potential for achieving cost-effective and stable photovoltaic devices.(5)In this work,a vapor-assisted solution method was introduced to fabricate high-purity perovskite film for use in efficient solar cells.To further reduce the electron-hole recombination and enhance charge extraction,we introduced the novel intermediate energy level of Mn S as hole transport layer(HTL)in Cs Pb Br3 perovskite solar cell(PKSC).The as-optimized Cs Pb Br3 PKSC based all inorganic transport layers delivers a PCE of 10.45% in comparison with 8.16% for the device free of intermediate layer,which is the highest PCE achieved among the Cs Pb Br3 based PKSC to date.Under challenging conditions,such as 80% relative humidity(RH)at 25?C or 85?C,the optimized device retained 90% PCE over 150 days or 80% over 90 days,compared to the initial efficiency,suggesting a good environmental tolerance to boost the commercial application of low-cost and high efficiency all-inorganic PKSCs.