Comparison of blended versus layered structures for poly(p-phenylene vinylene)-based polymer photovoltaics

Chasteen, S. V.; Härter, J. O.; Rumbles, G.; Scott, J. C.; Nakazawa, Y.; Jones, M.; Hörhold, H.-H; Tillman, H.; Carter, S. A.

doi:doi:10.1063/1.2168046

Volume/Page
Keyword
DOI
Citation
Advanced

Volume: Page/Article:

Search Content Type

article doi:

Citation:

Influence of lateral current spreading on the apparent barrier parameters of inhomogeneous Schottky diodes

The influence of the series resistance of inhomogeneous Schottky diodes on the apparent barrier parameters in three different arrangements was studied. It is shown that when there is a total current spreading in the semiconductor substrate the ideality factor of the diode remains unity and the extracted series resistance is equal to the real value. On the other hand a lack of current spreading in the substrate results in the different voltage drops on the particular series resistances which cau...

Nondispersive hole transport in carbazole- and anthracene-containing polyspirobifluorene copolymers studied by the charge-generation layer time-of-flight technique

Nondispersive hole transport in two polyspirobifluorene copolymers containing either 10% anthracene or 10% carbazole was studied in detail by the charge-generation layer time-of-flight (TOF) technique over a wide range of electric fields and temperatures. The TOF transients of both polymers showed a clear plateau indicating nondispersive transport of charge carriers. Zero-field mobilities were found to be in the order of 10−6 cm2/V s at room temperature. Results were analyzed within the framewo...

We characterize and compare blended and bilayered heterojunctions of polymer photovoltaic devices using poly[oxa-1,4-phenylene-1,2-(1-cyano)-ethenylene-2,5-dioctyloxy-1,4-phenylene-1,2-(2-cyano)-ethenylene-1,4-phenylene] (CN-ether-PPV) and poly[2,5-dimethoxy-1,4-phenylene-1,2-ethenylene-2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene-1,2-ethenylene] (M3EH-PPV) as electron- and hole-transporting polymers, respectively. We find that both blended and bilayered structures have substantially improved current densities (>3 mA/cm²) and power efficiencies ( ∼ 1% under white light) over neat films. Improved exciton dissociation at multiple interfaces and reduced recombination due to energy and charge transfers increases the charge-carrier collection in both types of heterojunction devices, but low electron mobilities in the polymers lead to low fill factors and reduced quantum efficiency ( ∼ 20%) that limit the power efficiency. Time-resolved photoluminescence reveals that for blended structures both the hole and electron-transporting polymers undergo efficient quenching with the exciton decay being dominated by the existence of two fast decay channels of 0.12 and 0.78 ns that are assigned to interspecies charge transfer and account for the increased short-circuit current observed. For layers, these components are not as prevalent. This result indicates that greater exciton generation at the dissociating interface and more efficient charge collection in the thin layers is primarily responsible for the improved short-circuit current, a conclusion that is further supported by numerical simulations of the exciton generation rate and charge collection. We also report evidence for an intermediate exciplex state in both types of structures with the greatest yield for blends with 50 wt % of CN-ether-PPV. Overall, the improved performance is due to different processes in the two structures; efficient bulk exciton quenching and charge transfer in blends and enhanced exciton generation and charge collection in layers. The optimization of each photovoltaic heterostructured device relies on this understanding of the mechanisms by which each material architecture achieves high power efficiencies.

Article Outline

INTRODUCTION
METHODS
RESULTS
1. Device characterization
  1. J-V curves and external quantum efficiency
  2. Absorption and steady-state photoluminescence
  3. Time-resolved photoluminescence
2. Modeling J-V characteristics of bilayer devices
  1. Simulation methods
  2. Parameters
  3. Results
CONCLUSIONS

RELATED DATABASES

To view database links for this article, you need to log in.

KEYWORDS and PACS

Keywords

polymers, photovoltaic cells, current density, excitons, electron-hole recombination, charge exchange, electron mobility, time resolved spectra, photoluminescence, radiation quenching

PACS

85.60.Bt

Optoelectronic device characterization, design, and modeling

ARTICLE DATA

Digital Object Identifier

http://dx.doi.org/10.1063/1.2168046

PUBLICATION DATA

ISSN

0021-8979 (print)

1089-7550 (online)

Publisher

$abstract.society.value is a Member of CrossRef

American Institute of Physics

For access to citing articles, you need to log in.

Figures (9) Tables (1)

Access to article objects (figures, tables, multimedia) requires a subscription; log in to view available files.
(Access to supplementary files, where available, is free for this journal.)