Interface Design to Improve the Performance and Stability of Solution‐Processed Small‐Molecule Conventional Solar Cells

Abstract

A systematic study on the effect of various cathode buffer layers on the performance and stability of solution-processed small-molecule organic solar cells (SMOSCs) based on tris{4-[5-(1,1-dicyanobut-1-en-2-yl)-2,2-bithiophen-5-yl]phenyl}amine (N(Ph-2T-DCN-Et) 3 ):6,6-phenyl-C71-butyric acid methyl ester (N(Ph-2T-DCN-Et) 3 :PC 70 BM) is presented. The power conversion effi ciency (PCE) in these systems can be signifi cantly improved from approximately 4% to 5.16% by inserting a metal oxide (ZnO) layer between the active layer and the Al cathode instead of an air-sensitive Ba or Ca layer. However, the low work-function Al cathode is susceptible to chemical oxidation in the atmosphere. Here, an amine group functionalized fullerene complex (DMAPA-C 60 ) is inserted as a cathode buffer layer to successfully modify the interface towards ZnO/Ag and active layer/Ag functionality. For devices with ZnO/DMAPA-C 60 /Ag and DMAPA-C 60 /Ag cathodes the PCEs are improved from 2.75% to 4.31% and to 5.40%, respectively, compared to a ZnO/Ag device. Recombination mechanisms and stability aspects of devices with various cathodes are also investigated. The signifi cant improvement in device performance and stability and the simplicity of fabrication by solution processing suggest this DMAPA-C 60 -based interface as a promising and practical pathway for developing effi cient, stable, and roll-to-roll processable SMOSCs.

High efficiency perovskite solar cells using a PCBM/ZnO double electron transport layer and a short air-aging step

“…In the first version of this p-i-n structure, the metal contacts (Al, Ag or Au) were directly evaporated onto the PCBM layer [16,18]. However, as demonstrated in organic solar cells, such a PCBM/metal contact is not optimized for electron extraction due to the energy level mismatch [21,22]. Therefore, interface engineering has been carried out between the PCBM and metal contact by inserting additional layers, such as thermally evaporated LiF [13], Ca [23], and C 60 /bathocuproine (BCP) [15], or solution processed poly[(9,9-bi s(30-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioct ylfluorene)] (PFN) [24], Bis-C 60 surfactant [17], TiO x [25], ZnO [26] etc.…”

Integrated molecular, morphological and interfacial engineering towards highly efficient and stable solution-processed small molecule solar cells

“…Nevertheless, the stability of the ZnO/Al based device is still quite poor owing to the instable Al cathode. 23 In the previous studies we have already demonstrated DMAPA-C 60 as a promising interlayer being compatible to a Ag cathode. 23 Here we introduced a new interfacial layer (PDINO) to modify the stable Ag cathode for expanding the currently rather limited choice of available electron transporting layers (ETLs) for small molecule OSCs (see Fig.…”

“…23 However, as compared to its polymeric counterparts, the development of interface layers applied in small molecule systems has largely been overlooked until recently. Therefore, the development of stable and effective device architectures based on interfacial engineering should be also highlighted in the photovoltaic optimization of SMOSCs.…”

Side‐Chain Engineering for Enhancing the Properties of Small Molecule Solar Cells: A Trade‐off Beyond Efficiency

“…[16,[29][30][31][32][33] Despite tremendous efforts have been made to enhance the stability of OSCs based on the consideration of extrinsic factors like reactions with oxygen and interface degradation, [3,16,24,[34][35][36] intrinsic reactions were less frequently reported due to the complexity of separating intrinsic versus extrinsic effects. [30,37] An important intrinsic mechanism is thermal degradation because an optimal BHJ morphology was frequently found to be a metastable state which readily moves toward a less efficient thermodynamic equilibrium state.…”