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<p>In this article, steady state and impedance spectroscopy (IS) is used to quantitatively understand the role of charge carrier dynamics on the performance of a bulk-heterojunction (BHJ) organic solar cell, with the active layer blend consisting of Poly-thieno[3,2b] thiophene-diketopyrrolopyrrole-co-thiophene as the donor and C70-butyric acid methyl ester as the acceptor (DPP-DTT:PC<sub>70</sub>BM). Optimized devices with an active layer thickness of ~220 nm show a fill factor (FF) of only 41%. Current density (<i>J</i>)–voltage (<i>V</i>) characteristics measured under dark as well as under varying light intensity indicate the presence of Shockley–Read–Hall recombination losses. IS carried out under open circuit conditions, under varying light intensity and varying bias voltages at 1 SUN illumination, further reveals high recombination losses. Furthermore, a low charge collection efficiency&#xa0; is obtained, which quantitatively explains the low FF in the studied BHJ solar cell. This is correlated with the low film quality of the solution-processed active layer, which is responsible for the presence of the trap states limiting the performance of the device.</p> Graphical abstract <p>This work investigates charge recombination losses and charge collection efficiency (CCE)&#xa0;in DPP-DTT:PC70BM bulk-heterojunction organic solar cells with relatively thick active layer thickness using impedance spectroscopy. The study identifies trap-assisted recombination which is correlated with poor film quality as key factors limiting CCE and consequently the device performance.</p>

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Investigation of charge recombination losses and charge collection efficiency in DPP-DTT:PC70BM based BHJ solar cell from impedance spectroscopy

  • 期刊论文

  • 发表日期：

    2026年6月15日

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  • Chandan V Gupta,
  • Sangita Bose

摘要

In this article, steady state and impedance spectroscopy (IS) is used to quantitatively understand the role of charge carrier dynamics on the performance of a bulk-heterojunction (BHJ) organic solar cell, with the active layer blend consisting of Poly-thieno[3,2b] thiophene-diketopyrrolopyrrole-co-thiophene as the donor and C70-butyric acid methyl ester as the acceptor (DPP-DTT:PC70BM). Optimized devices with an active layer thickness of ~220 nm show a fill factor (FF) of only 41%. Current density (J)–voltage (V) characteristics measured under dark as well as under varying light intensity indicate the presence of Shockley–Read–Hall recombination losses. IS carried out under open circuit conditions, under varying light intensity and varying bias voltages at 1 SUN illumination, further reveals high recombination losses. Furthermore, a low charge collection efficiency  is obtained, which quantitatively explains the low FF in the studied BHJ solar cell. This is correlated with the low film quality of the solution-processed active layer, which is responsible for the presence of the trap states limiting the performance of the device.

Graphical abstract

This work investigates charge recombination losses and charge collection efficiency (CCE) in DPP-DTT:PC70BM bulk-heterojunction organic solar cells with relatively thick active layer thickness using impedance spectroscopy. The study identifies trap-assisted recombination which is correlated with poor film quality as key factors limiting CCE and consequently the device performance.