Enhanced device performance via interfacial engineering in non-fullerene acceptor based organic solar cells

Abstract

Introduction of interface layers can maximize the performance of certain organic solar cells. We demonstrate that high efficiency non-fullerene acceptor based solar cells can be further improved with the insertion of PC70BM as an interlayer between the electron transport layer and the active layer. The combination of ZnO and PC70BM layers between a cathode and a bulk heterojunction active layer appears to serve as a better selective contact by reducing charge transport barrier and recombination. The enhanced short-circuit current density (JSC) is characterized by a low series-resistance (<2 Ω cm2), improved charge collection efficiency, and power conversion efficiency. These features are reflected in impedance spectroscopy and electrical noise measurements and provide a route for large-area organic solar cells.

Dominant Effect of UV-Light-Induced “Burn-in” Degradation in Non-Fullerene Acceptor Based Organic Solar Cells

“…Furthermore, UV-induced degradation causes a large drop in the device rectification ratio as compared to other degradation routes. These observations indicate the reduction in charge carrier extraction efficiency of the devices after accelerated aging stresses and correlate with the observed reduction in V OC and FF. ,, …”

“…These observations indicate the reduction in charge carrier extraction efficiency of the devices after accelerated aging stresses and correlate with the observed reduction in V OC and FF. 31,44,45 Additionally, a qualitative but clear trend of the acceptor molecule modifications near the ZnO interlayer with UV exposure was observed by studies during the fabrication process. UV-light was introduced on to the deposited layers during the fabrication procedure for 1 h duration.…”

“…Photocatalytic reaction of NFA in the presence of electron transport layer ZnO results in breaking of the double bond connecting electron-donating and -accepting groups within the acceptor molecule . It was shown that the presence of a high density of surface defects in low-temperature solution-processed ZnO and the UV-excitation results in the formation of hydroxyl radicals (·OH), which can decompose the vinyl group in ITIC and its derivative NFAs such as IT-4F. , This process can lead to breaking the conjugated structure and consequently weakens the charge transport, particularly at the interface with the interlayer . Similar results and features of the optimized devices with both types of ZnO (sol–gel method and nanoparticle dispersion) were observed.…”

“…Devices with PCE as high as 12% were obtained for these solar cells in our laboratory (Figure S2). 31 For the present studies, devices exhibiting >8% were chosen as the minimum PCE on which the degradation process was initiated. J−V of these devices was then monitored over a period of 10 h when UV exposure and thermal conditions were maintained on these devices in an inert atmosphere for 10 h. Figure 2 shows the normalized cell parameters including V OC , J SC , FF, and PCE of the devices which are exposed continuously to 1 sun (AM1.5G) illumination and 1 sun (AM1.5G) illumination with a UVcut filter (to remove UV components from the incident light) and subjected to continuous thermal stress of 70 °C for a 10 h duration.…”

Formation Mechanism of PFN Dipole Interlayer in Organic Solar Cells

“…[17] Works so far have focused on the topographical and electronic working mechanisms of these kinds of interlayers. [16,[20][21][22][23][24][25][26] Some works have also established important theoretical understandings on the surface chemical modification dynamics of some organic interlayers. [27][28][29] PFN (poly [(9, 9-bis(3 0 -(N, N-dimethylamino) propyl)-2, 7-fluorene)alt-2, 7-(9, 9-ioctylfluorene)]) is a kind of widely used water-/alcohol-soluble interfacial material in organic electronic devices.…”