Title

Quantifying recombination losses during charge extraction in bulk heterojunction solar cells using a modified charge extraction technique

RIS ID

111848

Publication Details

Wright, B., Nakajima, Y., Clarke, T. M., Okuda, K., Paananen, H., Mozer, A. J. & Mori, S. (2017). Quantifying recombination losses during charge extraction in bulk heterojunction solar cells using a modified charge extraction technique. Advanced Energy Materials, 7 (11), 1602026-1-1602026-9.

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.

Grant Number

ARC/DP110101369

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