Charge-carrier photogeneration and extraction dynamics of polymer solar cells probed by a transient photocurrent nearby the regime of the space charge-limited current

Abstract

To understand the complex behaviors of photogenerated charge carriers within polymer-based bulk-heterojunction-type solar cells, the charge-carrier photogeneration and extraction dynamics are simultaneously estimated using a transient photocurrent technique under various external-bias voltages, and a wide range of excitation intensities are analyzed. For this purpose, conventional devices with 80 nm thick active layers consisting of a blend of representative P3HT and PTB7 electron-donating polymers and proper electron-accepting fullerene derivatives were used. After the correction for the saturation behavior at a high excitation-intensity range nearby the regime of the space charge-limited current, the incident-photon-density-dependent maximum photocurrent densities at the initial peaks are discussed as the proportional measures of the charge-carrier-photogeneration facility. By comparing the total number of the extracted charge carriers to the total number of the incident photons and the number of the initially photogenerated charge carriers, the external quantum efficiencies as well as the extraction quantum efficiencies of the charge-carrier collection during a laser-pulse-induced transient photocurrent process were obtained. Subsequently, the charge-carrier concentration-dependent mobility values were obtained, and they are discussed in consideration of the additional influences of the charge-carrier losses from the device during the charge-carrier extraction that also affects the photocurrent-trace shape.

Graphical abstract

Keywords

charge-carrier photogeneration / transient photocurrent / polymer solar cells / charge-carrier extraction / space charge-limited current

References

[1] Krebs F C, Espinosa N, Hösel M, Søndergaard R R, Jørgensen M. Rise to power—OPV-based solar parks. Advanced Materials, 2014, 26(1): 29–39

[2] Jiang K, Wei Q, Lai J Y L, Peng Z, Kim H K, Yuan J, Ye L, Ade H, Zou Y, Yan H. Alkyl Chain tuning of small molecule acceptors for efficient organic solar cells. Joule, 2019, 3(19): 3020–3033

[3] Lin Y, Adilbekova B, Firdaus Y, Yengel E, Faber H, Sajjad M, Zheng X, Yarali E, Seitkhan A, Bakr O M, El-Labban A, Schwingenschlögl U, Tung V, McCulloch I, Laquai F, Anthopoulos T D. 17% efficient organic solar cells based on liquid exfoliated WS₂ as a replacement for PEDOT:PSS. Advanced Materials, 2019, 31(46): 1902965–1902965

[4] Yang W S, Park B W, Jung E H, Jeon N J, Kim Y C, Lee D U, Shin S S, Seo J, Kim E K, Noh J H, Seok S I. Iodide management in formamidinium-lead-halide–based perovskite layers for efficient solar cells. Science, 2017, 356(6345): 1376–1379

[5] Green M A. The path to 25% silicon solar cell efficiency: history of silicon cell evolution. Progress in Photovoltaics: Research and Applications, 2009, 17(3): 183–189

[6] Torto L, Cester A, Rizzo A, Wrachien N, Gevorgyan S A, Corazza M, Krebs F C. Model of organic solar cell photocurrent including the effect of charge accumulation at interfaces and non-uniform carrier generation. Journal of Electron Devices Society, 2016, 4(6): 387–395

[7] Menke S M, Ran N A, Bazan G C, Friend R H. Understanding energy loss in organic solar cells: toward a new efficiency regime. Joule, 2018, 2(1): 25–35

[8] Park H, An J, Song J, Lee M, Ahn H, Jahnel M, Im C. Thickness-dependent internal quantum efficiency of narrow band-gap polymer-based solar cells. Solar Energy Materials and Solar Cells, 2015, 143: 242–249

[9] Moulé J, Bonekamp J B, Meerholz K. The effect of active layer thickness and composition on the performance of bulk-heterojunction solar cells. Journal of Applied Physics, 2006, 100(9): 094503-1, 094503–094507

[10] Song J, Lee Y, Jin B, An J, Park H, Park H, Lee M, Im C. Connecting charge transfer kinetics to device parameters of a narrow band-gap polymer-based solar cell. Physical Chemistry Chemical Physics, 2016, 18(38): 26550–26561

[11] Cappel U B, Feldt S M, Schöneboom J, Hagfeldt A, Boschloo G. The influence of local electric fields on photo-induced absorption in dye sensitized solar cells. Journal of the American Chemical Society, 2010, 132(26): 9096–9101

[12] Pivrikas A, Sariciftci N S, Juska G, Österbacka R. A review of charge transport and recombination in polymer/fullerene organic solar cells. Progress in Photovoltaics: Research and Applications, 2007, 15(8): 677–696

[13] Gao Y, Pivrikas A, Xu B, Liu Y, Xu W, van Loosdrecht P H M, Tian W. Measuring electron and hole mobilities: charge selective CELIV. Synthetic Metals, 2015, 203: 187–191

[14] Park H, Jin B, Kim Y, Im C, An J, Park H, Tian W. Intensity-dependent transient photocurrent of organic bulk heterojunction solar cells. Journal of the Korean Physical Society, 2017, 70(2): 177–183

[15] Im C, Bässler H, Rost H, Hörhold H H. Hole transport in polyphenylenevinylene-ether under bulk photoexcitation and sensitized injection. Journal of Chemical Physics, 2000, 113(9): 3802–3807

[16] Bässler H, Köhler A. Unimolecular and supramolecular electronics: charge transport in organic semiconductors. Topics in Current Chemistry, 2012, 312: 1–65

[17] Howard I A, Hodgkiss J M, Zhang X, Kirov K R, Bronstein H A, Williams C K, Friend R H, Westenhoff S, Greenham N C. Charge recombination and exciton annihilation reactions in conjugated polymer blends. Journal of the American Chemical Society, 2010, 132(1): 328–335

[18] Di Nuzzo D, van Reenen S, Janssen R A J, Kemerink M, Meskers S C J. Evidence for space charge-limited conduction in organic photovoltaic cells at open-circuit conditions. Physical Review. B, 2013, 87(8): 085207-1, 085207–085211

[19] Cowan S R, Banerji N, Leong W L, Heeger A J. Charge formation, recombination, and sweep-out dynamics in organic solar cells. Advanced Functional Materials, 2012, 22(6): 1116–1128

[20] Hwang I, Greenham N C. Modeling photocurrent transients in organic solar cells. Nanotechnology, 2008, 19(42): 424012

[21] Credgington D, Durrant J R. Insights from transient optoelectronic analyses on the open-circuit voltage of organic solar cells. Journal of Physical Chemistry Letters, 2012, 3(11): 1465–1478

[22] Sudheendra Rao K, Mohapatra Y N. Open-circuit voltage decay transients and recombination in bulk-heterojunction solar cells. Applied Physics Letters, 2014, 104(20): 203303

[23] Miyake M, Nakajima H, Hemmi A, Yahiro M, Adachi C, Soh N, Ishimatsu R, Nakano K, Uchiyama K, Imato T. Performance of an organic photodiode as an optical detector and its application to fluorometric flow-immunoassay for IgA. Talanta, 2012, 96: 132–139

[24] Jahnel M, Thomschke M, Fehse K, Vogel U, An J D, Park H, Leo K, Im C. Integration of near IR and visible organic photodiodes on a complementary metaloxidesemi-conductor compatible backplane. Thin Solid Films, 2015, 592(Part A): 94–98

[25] Jŭska G, Genevǐcius K, Nekrǎsas N, Sliaŭzys G. Charge carrier transport, recombination, and trapping in organic solar cells studied by double injection technique. IEEE Journal of Selected Topics in Quantum Electronics, 2010, 16(6): 1764–1769

[26] McNeill C R, Hwang I, Greenham N C. Polaronic interaction of photocurrent transients in all-polymer solar cells: trapping and detrapping effects. Journal of Applied Physics, 2006, 106: 024507-1–024507-8

[27] Hahn T, Tscheuschner S, Kahle F J, Reichenberger M, Athanasopoulos S, Saller C, Bazan G C, Nguyen T Q, Strohriegl P, Bässler H, Köhler A. Monomolecular and bimolecular recombination of electronhole pairs at the interface of a bilayer organic solar cell. Advanced Functional Materials, 2017, 27(1): 1604906

[28] Valouch S, Nintz M, Kettlitz S W, Christ N S, Lemmer U. Thickness-dependent transient photocurrent response of organic photodiodes. IEEE Photonics Technology Letters, 2012, 24(7): 596–598

[29] Kniepert K, Neher D. Effect of the RC time on photocurrent transients and determination of charge carrier mobilities. Journal of Applied Physics, 2017, 122(19): 195501

[30] Kettlitz S W, Mescher J, Christ N S, Nintz M, Valouch S, Colsmann A, Lemmer U. Eliminating RC-effects in transient photocurrent measurements on organic photodiodes. IEEE Photonics Technology Letters, 2013, 25(7): 682–685

[31] Zhang D, Allagui A, Elwakil A S, Nassef A M, Rezk H, Cheng J, Choy W C H. On the modeling of dispersive transient photocurrent response of organic solar cells. Organic Electronics, 2019, 70: 42–47

[32] Bässler H. Charge transport in disordered organic photoconductors a Monte Carlo simulation study. Physica Status Solidi. B, Basic Research, 1993, 175(1): 15–56

[33] Gupta S K, Sharma A, Banerjee S, Gahlot R, Aggarwal N, Deepak, Garg A. Understanding the role of thickness and morphology of the constituent layers on the performance of inverted organic solar cells. Solar Energy Materials and Solar Cells, 2013, 116: 135–143

[34] Liu F, Zhao W, Tumbleston J R, Wang C, Gu Y, Wang D, Briseno A L, Ade H, Russell T P. Understanding the morphology of PTB7∙PCBM blends in organic photovoltaics. Advanced Energy Materials, 2014, 4(5): 1301377

[35] Longeaud C, Main C. Deconvolution of the transient photocurrent signals: application to the study of the density of states of a BTO crystal. Journal of Physics Condensed Matter, 2008, 20(13): 135217

RIGHTS & PERMISSIONS

Higher Education Press