Application Of Polymeric Materials As Hole Transporting Layer Of Perovskite Solar Cells

We have to rely on fossil fuels to get energy and it will eventually run out.Therefore we need to find sustainable energy.Sunlight is the most suitable sustainable energy,because its energy on the earth's surface far exceeds the world's energy consumption.Although inorganic solar cells such as silicon photovoltaic can harvest sunlight,they are expensive,cumbersome,and fragile,so they cannot be widely used.We prepared and characterized thin film solar cells.Among them,perovskite solar cells have a broad application prospect.In addition to being portable and cheap,they are comparable in efficiency to silicon solar cells.The inverted planar perovskite solar cell?p-i-n structure?has low temperature solution processability,and is more suitable for flexible substrate applications and batch production.The main obstacle for commercialization of perovskite solar cells is their poor stability.Therefore,in order to meet the market demand and industrialization of perovskite solar cells,we must constantly try to obtain safe and stable perovskite solar cells.Our main research goal is to use polymeric materials as the hole transport layer?HTL?of inverted perovskite solar cell?PSC?to improve its performance.Poly?triarylamine??PTAA?is currently the most effective HTL for inverted planar PSC,but its hole-mobility and wettability are low to obtain effective charge extraction and complete coverage of perovskite film on it respectively.In order to improve the hole-mobility of PTAA,we added poly?9,9-dioctyl fluoro-cobenzothiazole??F8BT?polymer to PTAA and used it as HTL of inverted planar PSC.This is the first time that F8BT has been introduced into PTAA matrix to prepare mixed polymer HTL for inverted planar PSC.Because of the low wettability of PTAA,the perovskite layer cannot be completely covered on it,so we used UV-ozone?UVO?treatment to improve the wettability of PTAA layer.We studied the effect of UVO-treated PTAA HTL on the performance of inverted planar PSCs and found that the average PCE of inverted planar PSCs based on UVO-treated PTAA HTL increased from 9.92%to 12.07%.UVO treatment can also improve the stability of unsealed PSCs under ambient conditions?58%humidity and 20°C?.UVO-treated polymer HTL not only improve the PCE of the inverted planar PSC,but also reduce hysteresis.The wettability of the PTAA layer after UVO treatment is significantly improved,while the electrical conductivity is slightly reduced.UVO treatment can increase the atmospheric stability of unsealed PSCs by approximately 20%.The results showed that UVO-treated PTAA HTL can promote the growth of perovskite crystals.Therefore,UVO treatment is an effective method to improve the wettability of hydrophobic surfaces to prepare high quality perovskite films on them.The most effective design for inverted planar perovskite solar cells is Si O₂/ITO/PTAA/Perovskite/Fullerene/BCP/Copper.The optimal concentration and preparation conditions of the PTAA layer depend on its molecular weight.Treatment on the PTAA layer can improve its conductivity and wettability,thereby improving device performance through better perovskite crystal growth.Spin coating method?one-step method or two-step method?and blade coating method can be successfully used for crystallization of perovskite layer on PTAA film.Various treatments on the perovskite layer can improve the crystal size,ion migration passivation,and PTAA film coverage for improving the performance of the inverted planar PSC.Both PC₆₁BM and/or C₆₀ can be used as effective ETL,while BCP is usually used as a buffer layer.In addition to Cu,Al and Ag can also be effectively used as back electrodes for inverted planar perovskite solar cells.Although PTAA is most effectively used as a HTL for inverted planar PSCs,it still has the disadvantages of low hole-mobility and wettability,which cannot achieve effective charge extraction and complete coverage of perovskite films on it,respectively.Most previous work had focused on doping PTAA HTL for inverted planar PSC with2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane?F4-TCNQ?and m-MTDATA.Therefore,the PCE of the inverted planar PSC improved by 18.24%.We used UVO treatment to improve the wettability of PTAA HTL.We treated the PTAA HTL layer with UVO for 20 seconds to obtain the required surface wettability to ensure the complete coverage of perovskite film on it.Then,we prepared PSCs containing mixed polymer HTLs?PTAA:F8BT?in different proportions,and characterized them to determine the optimal ratio of the mixed polymer as the HTL of the inverted planar PSC.Compared with pure PTAA HTL,PTAA:F8BT?2.5 wt%?HTL has higher conductivity and hydrophobicity without significantly affecting the light transmittance.The conductivity of the PTAA:F8BT?2.5 wt%?HTL increases significantly to the maximum,which is 48%stronger than that of pure PTAA film?10.2 vs.15.1?S/cm?.From the contact angle of water on PTAA and PTAA:F8BT?2.5 wt%?films?67°vs.80°?,we showed that after doping with F8BT?2.5 wt%?,the surface of the mixed polymer layer became more hydrophobic.The perovskite layer crystallized on PTAA:F8BT?2.5wt%?mixed polymer HTL also has better crystallinity and larger grain size.Due to above synergy,PSCs with PTAA:F8BT?2.5 wt%?mixed polymer HTL have improved PCE and enhanced stability.Compared with single polymer HTL,the PCE and atmospheric stability of unsealed PSC composed of mixed polymer HTL are both significantly improved by?30%.F8BT can also be introduced into other CTLs to optimize charge transfer,thereby promoting the development of high-performance PSCs.Compared with pure PTAA HTL,the maximum PCE of unsealed PSC with PTAA:F8BT?2.5 wt%?HTL increased by 29.82%,while the hysteresis was not obvious,and the stability was also improved by more than 30%.By incorporating F8BT?2.5 wt%?into the PTAA HTL,the inverted planar PSC is more effective than the commonly used F4-TCNQ-doped PTAA HTL?1 wt%?.Improved PTAA conductivity and optimized perovskite crystals are the main reasons for improving performance and stability.Due to smoother and more hydrophobic surface than pure PTAA,PTAA:F8BT?2.5 wt%?can make the contact quality of perovskite grain boundaries better.Therefore,the efficiency and stability of the inverted planar PSC with mixed polymer indicated that PTAA:F8BT?2.5 wt%?mixed polymer is an effective HTL for the inverted planar PSC.The main innovation of this work is the introduction of F8BT polymer into PTAA polymer to make PTAA:F8BT HTL and the use of UVO treatment to enhance the wettability of the PTAA layer.The use of PTAA:F8BT?2.5 wt%?mixed polymer HTL can significantly enhance the atmospheric stability of PSC,which is attributed to promoting the growth of perovskite crystals which not only increases the grain size,but also optimize grain boundaries.This work showed that adding F8BT?2.5 wt%?into PTAA as a mixed polymer HTL and UVO treatment to PTAA to improve wettability may be a potential method to improve the performance of inverted planar PSCs.It can also lead to the introduction of more suitable polymers as CTLs for the development of high-performance PSCs.