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Title: Photo annealing effect on p-doped inverted organic solar cell

We report the transient positive photo annealing effect in which over 600% boost of power conversion efficiency was observed in inverted organic photovoltaic devices (OPV) made from P3HT/PCBM by spray method, after 2 hrs of constant solar AM 1.5 irradiation at low temperature. This is opposite to usual photodegradation of OPV, and cannot be explained by thermal activation alone since the mere temperature effect could only account for 30% of the enhancement. We have investigated the temperature dependence, cell geometry, oxygen influence, and conclude that, for p-doped active layer at room temperature, the predominant mechanism is photo-desorption of O{sub 2}, which eliminates electron traps and reduces space charge screening. As temperature decreases, thermal activation and deep trap-state filling start to show noticeable effect on the enhancement of photocurrent at intermediate low temperature (T = 125 K). At very low temperature, the dominant mechanism for photo annealing is trap-filling, which significantly reduces recombination between free and trapped carriers. At all temperature, photo annealing effect depends on illumination direction from cathode or anode. We also explained the large fluctuation of photocurrent by the capture/reemit of trapped electrons from shallow electron traps of O{sub 2}{sup -} generated by photo-doping. Our study has demonstrated the dynamic process ofmore » photo-doping and photo-desorption, and shown that photo annealing in vacuum can be an efficient method to improve OPV device efficiency.« less
Authors:
; ; ;  [1]
  1. Department of Physics, University of South Florida, Tampa, Florida 33620 (United States)
Publication Date:
OSTI Identifier:
22304502
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 115; Journal Issue: 24; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; CAPTURE; CONVERSION; DESORPTION; DOPED MATERIALS; FLUCTUATIONS; ILLUMINANCE; IRRADIATION; ORGANIC SEMICONDUCTORS; ORGANIC SOLAR CELLS; OXYGEN; PHOTOVOLTAIC EFFECT; RECOMBINATION; SCREENING; SPACE CHARGE; SPRAYS; TEMPERATURE DEPENDENCE; TEMPERATURE RANGE 0273-0400 K; TRANSIENTS; TRAPPED ELECTRONS; TRAPS