Abstract
Electronic transport measurement using modulated photocurrent (MPC) spectroscopy is demonstrated herein in working organic photovoltaics (OPVs) before and after AM1.5G irradiation. OPVs with bulk heterojunction (BHJ) using prototypical donor and acceptor materials, poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1–2-b:4,5-b′]dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl] = hieno [3–4-b]thiophenediyl]] (PTB7) and [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM), were fabricated. The OPVs had inverted structures (BHJs are formed on transparent conductive oxide substrates). The photovoltaic performance of PTB7:PC71BM OPVs was characterized and the best power conversion efficiency was obtained at PTB7 content of 40 wt%. Electron and hole mobility were determined with MPC spectroscopy in PTB7:PC71BM OPVs and were well balanced at PTB7 content of 40 wt%. Degradation of the photovoltaic performance of PTB7:PC71BM OPVs with PTB7 content of 40 wt% caused by AM1.5G irradiation was studied. MPC spectroscopy showed that the well-balanced mobility was not affected by AM1.5G irradiation. The degradation of OPVs was not due to changes in the electronic transport properties, but mainly to the reduced short circuit current (Jsc) and fill factor (FF). The origin of this reduction is discussed.
Highlights
Organic semiconductor thin films have unique properties such as flexibility, printability, and low cost, and organic photovoltaics (OPVs) can be formed on curved surfaces and flexible substrates for the power sources of mobile devices and applied to light sensing for biological sensors [1].High power conversion efficiency (PCE) has been achieved using bulk heterojunction (BHJ), a mixture of donor and acceptor organic semiconducting materials [1]
We study the degradation of electronic transport properties of inverted OPVs before and after simulated sunlight (AM1.5G) exposure by means of a modulated photocurrent spectroscopy (MPC) technique [17]
We studied the electronic transport properties of working PTB7:phenyl C71 butyric acid methyl ester (PC71 BM) OPVs with inverted configuration using MPC spectroscopy before and after AM1.5G irradiation
Summary
Organic semiconductor thin films have unique properties such as flexibility, printability, and low cost, and organic photovoltaics (OPVs) can be formed on curved surfaces and flexible substrates for the power sources of mobile devices and applied to light sensing for biological sensors [1]. Degradation mechanisms in OPV are generally complicated and include a variety of processes: photo-bleaching of the photoactive layer and trap generation [14,15], degradation of the hole conducting PEDOT:PSS layer [16], ion migration from the electrodes, and morphological changes of the device [14]. These processes are induced simultaneously by exposing OPVs to sunlight and are almost inseparable. BHJ is shorter than that of inverted OPVs with P3HT:PCBM BHJ and the degradation process of PTB7:PC71 BM OPVs can be observed, we studied the degradation process of inverted OPVs with PTB7:PC71 BM BHJ
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