Inverted Polymer Solar Cells with Reduced Interface Recombination

Abstract

Interface recombination induced by the defect states in zinc‐oxide‐nanoparticle‐based electron extraction layer is reported as a significant loss‐mechanism of photocurrent collection. By choosing appropriate UV–ozone treatment conditions on the zinc oxide layer, inverted polymer solar cells show reduced interface recombination and thus improved power conversion efficiencies of up to 8.1%.

Ethanedithiol Treatment of Solution‐Processed ZnO Thin Films: Controlling the Intragap States of Electron Transporting Interlayers for Efficient and Stable Inverted Organic Photovoltaics

“…[14,[47][48] As reported by So and co-workers, UV-ozone treatment not only passivates the surface defects but also generates excess oxygen at the ZnO surfaces which may oxidize the polymers with higher-lying HOMO energies, such as P3HT, and hence degrade the device performance. [14] Upon successful attempts of EDT passivation on ZnO nanocrystal films, we further extended the EDT passivation approach to the ZnO films deposited from Sol-gel precursors. Inverted organic solar cells based on Sol-gel derived and EDT treated ZnO films were fabricated using either the P3HT: PC61BM blends or TQ1: PC71BM blends as active layers.…”

“…As shown in Figure 4b, the PL spectrum (excitation: 310 nm) of the P-ZnO film exhibits a narrow emission peak at ~366 nm corresponding to the band-edge emission and a board peak of visible emission centered at ~545 nm, which is attributed to the defect-related emission. [14,38] After EDT treatment, both the visible emission and the band-edge emission are almost completely quenched. We note that a similar PL quenching phenomenon was observed for the dodecanethiol modified ZnO nanocrystal films.…”

“…[10][11][12][13] Despite the successes of applying solution-processed ZnO ETLs in inverted OPVs, a major challenge lies in how to control the intragap states induced by surface defects. [14,15] Lowtemperature and solution-processed ZnO ETLs generally have high densities of surface defects such as dangling bonds and surface groups, introducing various intragap energy levels.…”

“…[18] A few strategies have been developed to passivate the surface defects of solution-processed ZnO ETLs. [14,16,[19][20][21][22][23] For example, employing self-assembled monolayers (SAMs) on top of ZnO films can avoid the direct contact between ETLs and active layers. The introduction of SAMs may result in formation of interfacial dipoles that favor electron extraction.…”

UV-Induced Oxygen Removal for Photostable, High-Efficiency PTB7-Th:PC71BM Photovoltaic Cells

“…Provided that the Voc did not change except for exposure times larger than 20 min, as seen in Figure 2E, we concluded that the 20 min UVN treatment led to the largest PCE as seen in Table S1. Such optimal performance was attributed to enhanced conductivity of the ZnO ETL and reduced interface recombination 29,34 , which was confirmed by the I-V 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 conductivity measurements from diode devices of ITO/ZnO (w/o UVN treatment) (100 nm)/Al, as shown in Figure S2. The electrical conductivity under illumination for UVNtreated ZnO film was ~ 4.16×10 -4 S/m, about 1.5 times higher than the one from as-prepared ZnO film.…”