Reducing Burn‐In Loss of Organic Photovoltaics by a Robust Electron‐Transporting Layer

Abstract

efficiency (PCE) of OPVs has already reached 14.2%. [1] However, a major drawback for the commercialization of OPVs is their long-term stability under continuous operation. Especially, OPVs suffer from a rapid decrease in PCE during initial device operation, which is known as the "burn-in loss." [2][3][4][5][6] The origin of the burn-in loss is thought to be mainly related to the instability of the bulk heterojunction (BHJ) morphology and/or interface rather than the photo-oxidation of the photoactive layer.Morphological instability of photoactive layer is one of critical issues of burn-in loss in OPV. [7][8][9][10][11] Because electron-donating and electron-accepting materials are blended in a photoactive layer to form metastable BHJ, applying high-temperature heat or strong light can cause microscopic morphology changes resulting in the burn-in loss. [8,9] For typical OPVs utilizing a BHJ, a photoactive layer (blend of electrondonating conjugated polymer and electron-accepting fullerene) is sandwiched between two electrodes (anode/cathode) with their corresponding charge-transporting (hole/electron) interlayers. [12] The interlayers minimize the energy barrier between the photoactive layer and electrodes, and thereby enhance the collection efficiencies of electrons/holes on the cathode/ anode. Thus, significant efforts have been made to develop various electron-transporting layer (ETL) materials for OPVs such as transition metal oxides, [13] carbon-based materials, [14] polymers, [15] low work function metal salts, [16] and organicinorganic hybrids. [17] Among various ETL materials, transition metal oxides are commonly utilized because of their adequate highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels, stability, transparency, and excellent electron mobility. [5,18] Additionally, transition metal oxide ETLs provide an excellent barrier property against oxygen and metal electrode diffusion compared to organic ETL materials. Various types of transition metal oxides such as zinc oxide (ZnO), [19] titanium oxide (TiO 2 or TiO x ), [20][21][22] tin oxide (SnO 2 or SnO x ), [23] and niobium oxide (Nb 2 O 5 or NbO x ) [24] have been explored for use as ETL materials for OPVs. Generally, the transition metal oxide layer is deposited by vacuum deposition techniques such as sputtering, [22] atomic layer deposition, [25] or It is revealed that instability of interface between photoactive layer and electron-transporting layer (ETL) is one of the causes of the rapid degradation of organic photovoltaics (OPV) performance during initial operation (burn-in loss) under the light soaking. The stability of OPV is greatly enhanced by applying a robust ETL composed of TiO 2 nanoparticles (TNPs). The TNPs bound with π-π interactive 3-phenylpentane-2,4-dione (TNP-Ph) form more robust ETLs than those bound with van der Waals interactive 3-methyl-2,4pentanedione TNP (TNP-Me). The OPV with TNP-Ph maintains 73% of its initial power conversion efficiency (PCE) after 1000 h of light soa...

Top‐Gate Field‐Effect Transistor as a Testbed for Evaluating the Photostability of Organic Photovoltaic Polymers

“…[ 20,21 ] Finally, a major degradation factor in OSCs is light irradiation. [ 22–25 ] This is one of the most crucial concerns for OSCs in the sense that i) light irradiation is inevitable during OSC operation and ii) it accelerates the other intrinsic/extrinsic degradation attributes listed earlier. [ 26 ] Furthermore, light‐induced performance degradation predominantly occurs in the early stages of the OSC's operation, leading to an abrupt decrease in its initial performance known as “burn‐in” loss and decreasing the device lifetime considerably.…”

“…These photochemical and photophysical mechanisms causing photo‐instability in OSCs are found to be strongly dependent on the material's properties. [ 22,25,35 ] Therefore, developing donor and acceptor materials that are more resistant to light irradiation would be the most effective way to reduce the “burn‐in” loss in OSCs. However, achieving this is not straightforward.…”

A levelized cost of energy approach to select and optimise emerging PV technologies: The relative impact of degradation, cost and initial efficiency

“…Burn-in may be caused by morphological changes in the blended materials of the active layer of emerging PV devices when exposed to light or heat [54,55], as well as by the interfacial resistance between the electron-transporting layer (ETL) and the photoactive layer [20]. On the other hand, linear degradation is mainly caused by the ingress of water and oxygen to the device, which under illumination can react with the organic layers, resulting in photo-bleaching or minimal light-absorption ability [53].…”