Significant Stability Enhancement in High-Efficiency Polymer:Fullerene Bulk Heterojunction Solar Cells by Blocking Ultraviolet Photons from Solar Light.

Jaehoon Jeong,Hwajeong Kim,Donal D C Bradley,Hyemi Han,Jooyeok Seo,Sungho Nam,Thomas D Anthopoulos,Youngkyoo Kim

doi:10.1002/advs.201500269

Abstract

Achievement of extremely high stability for inverted‐type polymer:fullerene solar cells is reported, which have bulk heterojunction (BHJ) layers consisting of poly[4,8‐bis(5‐(2‐ethylhexyl)thiophen‐2‐yl)benzo[1,2‐b:4,5‐b′]dithiophene‐alt‐3‐fluorothieno[3,4‐b]thiophene‐2‐carboxylate] (PTB7‐Th) and [6,6]‐phenyl‐C71‐butyric acid methyl ester (PC71BM), by employing UV‐cut filter (UCF) that is mounted on the front of glass substrates. The UCF can block most of UV photons below 403 nm at the expense of ≈20% reduction in the total intensity of solar light. Results show that the PTB7‐Th:PC71BM solar cell with UCF exhibits extremely slow decay in power conversion efficiency (PCE) but a rapidly decayed PCE is measured for the device without UCF. The poor device stability without UCF is ascribed to the oxidative degradation of constituent materials in the BHJ layers, which give rise to the formation of PC71BM aggregates, as measured with high resolution and scanning transmission electron microscopy and X‐ray photoelectron spectroscopy. The device stability cannot be improved by simply inserting poly(ethylene imine) (PEI) interfacial layer without UCF, whereas the lifetime of the PEI‐inserted PTB7‐Th:PC71BM solar cells is significantly enhanced when UCF is attached.

Highlights

Achievement of extremely high stability for inverted-type polymer:fullerene solar cells is reported, which have bulk heterojunction (BHJ) layers consisting of poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b′]dithiophenealt-3-fluorothieno[3,4-b]thiophene-2-carboxylate] (PTB7-Th) and [6,6]-phenyl-Great attention has been paid to organic solar cells for the last two decades because of their advantages, including easy tailoring of solar light absorptionC71-butyric acid methyl ester (PC71BM), by employing UV-cut filter (UCF)with various organic materials and low that is mounted on the front of glass substrates
To examine whether the reduced (≈20%) light intensity influenced the slow change of J–V curves for the device with UCF, the device without UCF was subject to the stability test under illumination with the solar light with the reduced intensity
The stability of PTB7-Th:phenyl-C71-butyric acid methyl ester (PC71BM) solar cells with and without UCF was investigated under continuous illumination with a simulated solar light

Summary

Introduction

Achievement of extremely high stability for inverted-type polymer:fullerene solar cells is reported, which have bulk heterojunction (BHJ) layers consisting of poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b′]dithiophenealt-3-fluorothieno[3,4-b]thiophene-2-carboxylate] (PTB7-Th) and [6,6]-phenyl-. The device stability cannot be improved by inserting poly(ethylene imine) (PEI) interfacial layer works for the bulk heterojunction (BHJ) concept and the BHJ nanomorphology control.[17,18,19,20,21,22,23,24,25] Interestingly, most of the high-efficiency (>8%) organic solar cells are fabricated with blends of conjugated without UCF, whereas the lifetime of the PEI-inserted PTB7-Th:PC71BM solar polymers and soluble fullerenes, the cells is significantly enhanced when UCF is attached. We have attempted to block the UV light from the simulated solar radiation by employing a UV-cut filter (UCF) (cutoff = 405 nm) and examined the stability of polymer:fullerene solar cells with BHJ layers of PTB7-Th and [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM). The PTB7Th:PC71BM solar cells with poly(ethylene imine) (PEI) interfacial dipole layers were fabricated and subjected to the stability test

Results and Discussion

Conclusion

Experimental Section