Study Of Organic Solar Cells With The Optimized Electron Transport Layer

The basic configuration of organic solar cells is a sandwich structure of five layers,the middle active layer traps photons and generates charges,and the electrodes on both sides are responsible for the collection of electrons and holes.The electrons and holes transfer from active layer to electrodes through the intermediate layers.The two charge transport layers plays an important role on the device performance,which directly influence of optical and electrical properties of the device.For the inverted organic solar cell,transition metal oxide TiO₂ and ZnO are usually used as the electron transporting layer.Although transition metal oxides own the ability of blocking holes,the property itself has also affect the conductive ability,which will reduce the transmission efficiency and then decrease the electron collection efficiency of the cathode.Firstly,the significantly enhanced performance uponincorporation of Au nanoarrows in solution-processed organic photovoltaic devices is demonstrated in this study.Incorporating Au nanoarrows into the Zn O cathode buffer layer results in superior broadband optical absorption improvement and a power conversion efficiency of 7.82%is realized with a 27.3%enhancement compared with the control device.The experimental and theoretical results indicate that the introduction of Au nanoarrows not only increases optical trapping by the SPR effect but also facilitates exciton generation,dissociation,and charge transport inside the thin film device.The results of J_sc and EQE measurements reveal that Au NAs significantly improve light-harvesting in the visible range,yielding a PCE enhancement.Incorporation of the Au NAs improved the charge transport and collection properties,which guarantees the better performance of doping devices.Also,the addition of high conductivity Au NAs resulted in low series resistance and larger resultant photocurrent.Second,in this contribution,a series of conducting polyfluorenes（PF）are introduced to improve interface adhesion and boost charge extraction of the TiO₂ electron transport layer of inverted polymer solar cells（PSCs）.After employing poly（9,9-dihexylfluorenyl-2,7-diyl）（PDF）,poly[（9,9-dioctylfluorenyl-2,7-diyl）-altco-（1,4-benzo-{2,10,3}-thiadiazole）]（PDFBT）,and poly[（4-（5-（7-methyl-9,9-dioctyl-9H-fluoren-2-yl）hiophen-2-yl）-7-（5-methyl thiophen-2-yl）benzo[c][1,2,5]hiad-iazole）]（PFTBT）as capping layers,interfacial coherence improvement and energy loss decrease are both achieved,facilitating charge transfer from the active layer to the TiO₂ layer.The optimized contact,enhanced electrical conductivity,and reduced internal resistance contribute to increased short-circuit current density and fill factor,leading to an enhanced power conversion efficiency（PCE）from 5.72%up to 7.97%.The employment of the PF capping TiO₂ buffer layer provides a promising approach to develop high efficiency PSCs.The utilization of the PF capping layer can apparently improve the energy level alignment and increase roughness of the Ti O₂ surface,which provide effective interface contact and interfacial adhesion between the TiO₂ and active layers.The facilitated charge transport and minimized contact resistance reduced the energy barrier,resulting in a higher photocurrent.This study paves a facile way to enhance device performance of inverted PSCs.At last,the electron transport layer plays a crucial role on determining electron injection and extraction,resulting from the effect of balancing charge transport and reducing the interfacial energy barrier.Decreasing the inherent incompatibility and enhancing electrical contact via employing appropriate buffer layer at the interface of hydrophobic organic active layer and hydrophilic inorganic electrode are also essential for charge collection.Herein,we demonstrate that an efficient dual polyelectrolytes interfacial layer composed of polyethylenimine（PEI）and conducting poly（9,9–dihexylfluorenyl-2,7-diyl）（PDHFD）is incorporated to investigate the interface energetics and electron transport in bulk heterojunction（BHJ）polymer solar cells（PSCs）.The composited PEI/PDHFD interface layer（PPIL）overcomed the low conductivity of bare PEI polymer,which decreased series resistance and facilitated electron extraction at the ITO/PPIL–active layer interface.The introduction of the interface energy state of the PPIL reduced the work function of ITO so that it can match the top of the valence band of the photoactive materials and promoted the formation of ohmic contact at ITO electrode interface.As a result,the composited PPIL tuned energy alignment and accelerated the electron transfer,leading to significantly increased photocurrent and power conversion efficiency（PCE）of the devices based on various representative polymer:fullerene systems.Therefore,the electron transport layer interface optimization design method of organic solar cell was presented in this work,which provides effective scientific basis for the production of a wide range of applications in organic solar cells,it is also the key technology to solve the problem of inverted organic solar cell applications and has the important research significance.