Efficient organic solar cells with low-temperature in situ prepared Ga 2 O 3 or In 2 O 3 electron collection layers
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Published online 13 November 2020 | https://doi.org/10.1007/s40843-020-1514-3
Efficient organic solar cells with low-temperature in situ prepared Ga2O3 or In2O3 electron collection layers 1
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Yiming Bai , Rongkang Shi , Yinglong Bai , Fuzhi Wang , Jun Wang , Tasawar Hayat , 4 1,2* Ahmed Alsaedi and Zhan’ao Tan ABSTRACT Facile synthesis of an interfacial layer in organic solar cells (OSCs) is important for broadening material designs and upscaling photovoltaic conversion efficiency (PCE). Herein, a mild solution process of spin-coating In(acac)3 and Ga(acac)3 isopropanol precursors followed by low-temperature thermal treatment was developed to fabricate In2O3 and Ga2O3 cathode buffer layers (CBLs). The introduction of In2O3 or Ga2O3 CBLs endows PM6:Y6-based OSCs with outstanding performance and high PCEs of 16.17% and 16.01%, respectively. Comparison studies present that the In2O3 layer possesses a work function (WF) of 4.58 eV, which is more favorable for the formation of ohmic contact compared with the Ga2O3 layer with a WF of 5.06 eV and leads to a higher open circuit voltage for the former devices. Electrochemical impedance spectroscopy was performed to reveal how In2O3 and Ga2O3 affect the internal charge transfer and the origin of their performance difference. Although In2O3 possesses lower series resistance loss, Ga2O3 has a higher recombination resistance, which enhances the device fill factor and compensates for its series resistance loss to some extent. Comparative analysis of the photo-physics of In2O3 and Ga2O3 suggests that both are excellent CBLs for highly efficient OSCs. Keywords: organic solar cells, cathode buffer layer, In2O3, Ga2O3, charge transfer
INTRODUCTION Organic solar cells (OSCs) with merits of low-cost solution processability, high efficiency, and more than 10 years of predicted lifetime are currently considered promising technology for obtaining sustainable energy in the future [1–3]. Benefiting from the delicate electron-
donor/acceptor material design and diverse device engineering, the certified photovoltaic conversion efficiency (PCE) of the state-of-the-art single junction OSC devices has recently reached 17% [4], which motivates extensive interest in the academia and industry. In general, OSCs are based on a bulk-heterojunction structure where the blended photoactive materials sandwich between a cathode buffer layer (CBL) and an anode buffer layer (ABL) to selectively facilitate charge extraction and minimize interfacial recombination loss, thereby boosting the device efficiency [5–7]. Consequently, synthesizing a novel appropriate interfacial layer is crucial for the development of efficient photovoltaic cells [8]. An ideal CBL in inverted OSCs (i-OSCs), which exhibit superior environmental stability to traditional OSCs, should possess facile solution-processible synthesis, suitable work function (WF), and favorable optical/electrical/morphological features to upscale device performance [9–11]. In the past decade, various n-type metal oxides, such as ZnO [12–14],
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