Quantifying Recombination Losses during Charge Extraction in Bulk Heterojunction Solar Cells Using a Modified Charge Extraction Technique. Issue 11 (12th January 2017)

• Record Type: Journal Article
• Authors: Wright, Brendan; Nakajima, Yukihiro; Clarke, Tracey M.; Okuda, Kouichi; Paananen, Heikki; Mozer, Attila J.; Mori, Shogo
• Is Part Of: Advanced energy materials. Volume 7:Issue 11(2017)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2017-01-12
• Subjects: charge transport -- energy levels -- lifetime -- mobility -- recombination coefficient; Energy harvesting -- Materials -- Periodicals; Energy conversion -- Materials -- Periodicals; Energy storage -- Materials -- Periodicals; Photovoltaics -- Periodicals; Fuel cells -- Periodicals; Thermoelectric materials -- Periodicals; 621.31
• DOI: 10.1002/aenm.201602026
• Languages: English
• ISSNs: 1614-6832

Abstract

Abstract : A variety of charge extraction (CE) techniques have been developed to measure charge density and recombination coefficients in bulk heterojunction solar cells. Charge recombination during charge extraction as a major limitation of this method has not been systematically quantified. This study reports CE measurements using a newly designed fast switch, which enables the application of a reverse bias to the solar cells facilitating charge extraction. With applied reverse bias, more than 40% increase in the extracted charge is obtained in solar cells with thicker active layers or with fast recombination. The measured charge carrier lifetime increases by up to a factor of three at sufficiently high applied biases (up to 8 V), suggesting significant errors in CE measurements without applied bias. The increased extracted charges with increasing applied bias are attributed to a combination of three cases: (i) slightly faster charge extraction due to the larger electric field; (ii) increased charge extraction rate at high light intensities when the transients are space charge disturbed; (iii) increased charge separated lifetime during charge extraction attributed to the spatial separation of the electron and hole density due to the applied electric field. Abstract : Reverse bias during charge extraction is applied through a fast switch to bulk heterojunction solar cells. More than 40% increase in the extracted charge is seen and the recombination lifetime obtained from the relation between the extracted charge and switching delay time is increased up to three times, showing the importance of reverse bias to measure lifetime.