Development of Efficient and Stable Inverted Bulk Heterojunction (BHJ) Solar Cells Using Different Metal  Oxide Interfaces

Litzov, Ivan; Brabec, Christoph J.

doi:10.3390/ma6125796

Cited by 63 publications

(45 citation statements)

References 79 publications

(273 reference statements)

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“…Among the n-type metal oxides used in inverted PSCs, ZnO is an interesting interfacial material due to its high transparency in Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/solmat the visible range, relatively high electron mobility, appropriate energy band structure and environmental stability [21][22][23][24]. ZnO has also the advantage to act as hole blocking layer because its valence band is much lower than those of the highest occupied molecular orbital of the materials (polymers and fullerenes) usually employed in the realization of the blend.…”

Section: Introductionmentioning

confidence: 99%

Influence of annealing treatments on solution-processed ZnO film deposited on ITO substrate as electron transport layer for inverted polymer solar cells

Morvillo

Diana

Mucci

et al. 2015

Solar Energy Materials and Solar Cells

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Section: Introductionmentioning

confidence: 99%

Influence of annealing treatments on solution-processed ZnO film deposited on ITO substrate as electron transport layer for inverted polymer solar cells

Morvillo

Diana

Mucci

et al. 2015

Solar Energy Materials and Solar Cells

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“…Consequently, compatible HT IFLs have been developed to tune their valence band minima (VBM) or HOMO energies to match that of a specific organic donor. In contrast, because of historical limitations in acceptor diversity, far less effort has been devoted to developing ET IFLs-to date, a few ET IFLs have been used in inverted OPVs, primarily TiO x , ZnO x , several polymers, self-assembled monolayers, and cross-linked fullerenes (11,(14)(15)(16)(20)(21)(22)(23)(24). Nevertheless, most of these materials have fixed band edge positions, significantly limiting their adaptability to emerging OPV materials systems with acceptors having different LUMO energies.…”

mentioning

confidence: 99%

Amorphous oxide alloys as interfacial layers with broadly tunable electronic structures for organic photovoltaic cells

Zhou

Kim

Loser

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

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In diverse classes of organic optoelectronic devices, controlling charge injection, extraction, and blocking across organic semiconductor-inorganic electrode interfaces is crucial for enhancing quantum efficiency and output voltage. To this end, the strategy of inserting engineered interfacial layers (IFLs) between electrical contacts and organic semiconductors has significantly advanced organic light-emitting diode and organic thin film transistor performance. For organic photovoltaic (OPV) devices, an electronically flexible IFL design strategy to incrementally tune energy level matching between the inorganic electrode system and the organic photoactive components without varying the surface chemistry would permit OPV cells to adapt to ever-changing generations of photoactive materials. Here we report the implementation of chemically/environmentally robust, low-temperature solution-processed amorphous transparent semiconducting oxide alloys, In-Ga-O and Ga-Zn-Sn-O, as IFLs for inverted OPVs. Continuous variation of the IFL compositions tunes the conduction band minima over a broad range, affording optimized OPV power conversion efficiencies for multiple classes of organic active layer materials and establishing clear correlations between IFL/photoactive layer energetics and device performance.interface | amorphous oxide | photovoltaic | interfacial layers S olar to electrical energy conversion technologies have received great attention as abundant and sustainable resources (1-5). The diffuse nature of solar energy requires low-cost, largearea devices while maintaining high power conversion efficiency (PCE) (3). As a universal design strategy, many of the emerging thin film photovoltaic (PV) technologies such as bulk heterojunction (BHJ) organic, perovskite, quantum dot (QD), and CIGS (Cu-InGa-Se) solar cells are fabricated using a trilayer architecture, where light absorbers are sandwiched between two electrodes coated with various interfacial layers (IFLs) (6-9). Stringent requirements govern ideal IFL materials design. Energetically, their respective band positions should match those of the photoinduced built-in potentials to provide energetically continuous carrier transport pathways and to accommodate the maximum allowed output voltage. In recent reports, PV performance enhancement via IFL energetic tuning has been demonstrated for very specific BHJ organic, QD, and perovskite cell compositions (6,8,10,11). However, true IFL energetic tunability has not been achieved and offers a challenging opportunity to optimize device performance.Fabricable from energetically diverse organic active layers, organic photovoltaics (OPVs) provide an excellent test bed for tuning IFL energetics and are the subject of this study. The basic BHJ OPV architecture contains a mesoscopically heterogeneous and isotropic, phase-separated donor-acceptor blend-a strategy to overcome the relatively short exciton diffusion lengths (∼10 nm) (2, 12, 13), sandwiched between hole-transporting (HT) and electron-transporting (ET) IFLs (2). Th...

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“…Because such metal oxides have specifi c energy levels to only transfer electrons, their operation as ETLs is compatible with their excellent electron-transporting and hole-blocking characteristics. [ 2,3,9,10 ] Numerous synthetic processes have been developed for those metal oxide systems. In particular, sol-gel synthesis of those metal oxide systems has received intense attention because of its simple solution process for uniform fi lm formation at room temperature (RT).…”

mentioning

confidence: 99%

“…Recently, the power conversion effi ciency (PCE) of PSCs has exceeded the 10% mark that has been considered the barrier for its commercialization. [1][2][3] In general, PSCs have adapted a regular device structure in which the BHJ photoactive layer is located between the transparent indium-tin oxide (ITO) bottom anode (for collecting holes) and the top cathode using lower work-function (WF) metals, such as aluminum (Al) or calcium (Ca), for collecting electrons. However, the vacuum deposition process of the top metals in regular PSCs is not compatible with the realization of "printable photovoltaics," which is the ultimate goal of PSCs.…”

mentioning

confidence: 99%

Overcoming the Light‐Soaking Problem in Inverted Polymer Solar Cells by Introducing a Heavily Doped Titanium Sub‐Oxide Functional Layer

Kim

Kong

Kim

et al. 2014

Advanced Energy Materials

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into the ITO electrode. [5][6][7][8] One of the promising ETLs is a class of materials known as solution-based metal oxide systems, such as titanium sub-oxide (TiO x ) and zinc oxide (ZnO). Because such metal oxides have specifi c energy levels to only transfer electrons, their operation as ETLs is compatible with their excellent electron-transporting and hole-blocking characteristics. [ 2,3,9,10 ] Numerous synthetic processes have been developed for those metal oxide systems. In particular, sol-gel synthesis of those metal oxide systems has received intense attention because of its simple solution process for uniform fi lm formation at room temperature (RT). When sol-gel processed TiO x (or ZnO) is coated between ITO and the BHJ layer, the layer acts as an ETL in i-PSCs by aligning energy levels and selecting only electron transport. However, because of the low carrier density or the many trap sites in the semiconducting metal oxide, a Schottky barrier develops at the high WF-metal/metal-oxide interface or energy level mismatching at the metal oxide/BHJ layer interface becomes a recurring issue. [9][10][11][12][13][14][15] Those problems hinder the electron transport between the BHJ layer and ITO and result in the extremely low device performance in i-PSCs, as shown in Figure 1 a. [9][10][11][12]14,15 ] Although photo-excitation of the metal oxides by UV-irradiation increases the carrier density in the metal oxides and recovers the device performance by narrowing and lowering the depletion barrier, as in Figure 1 b, through a so-called a "lightsoaking process," such a photoreduction process takes several minutes and the absence of UV light irradiation (for example, UV protection coating etc.) would be critical for practical applications. [9][10][11][12][13][14][15] Although many researchers have tried to fi nd a fundamental solution to remove the light-soaking process of the metal oxides in the i-PSCs, there has been no successful approach that is directly applicable to printable photovoltaics.The light-soaking process in i-PSCs with the TiO x ETL implies that the increased carrier density in TiO x by chemical doping can be a fundamental solution for this problem. In general, doping the titanium oxide system precedes the reduction process, for example nitrogen (N) doping of titanium dioxide (TiO 2 ). When titanium-oxygen (Ti-O) bonds are replaced with the titanium-nitrogen (Ti-N) bonds, it is well known that the carrier density of TiO 2-δ N δ substantially increases. [16][17][18][19] However, because the formation of the Ti-O bonds is a predominant process in the typical sol-gel method, it has been impossible to control the doping process in the sol-gel fabrication of the metal oxide systems. [ 18,[20][21][22] Such a diffi culty in the doping process often requires additional purifi cations of the sol-gel processed metal oxides, for example, washing or heating processes. [ 18,[21][22][23] Bulk heterojunction (BHJ) polymer solar cells (PSCs) continue to be a promising approach for low-cost energy harvesting becau...

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Development of Efficient and Stable Inverted Bulk Heterojunction (BHJ) Solar Cells Using Different Metal Oxide Interfaces

Cited by 63 publications

References 79 publications

Influence of annealing treatments on solution-processed ZnO film deposited on ITO substrate as electron transport layer for inverted polymer solar cells

Influence of annealing treatments on solution-processed ZnO film deposited on ITO substrate as electron transport layer for inverted polymer solar cells

Amorphous oxide alloys as interfacial layers with broadly tunable electronic structures for organic photovoltaic cells

Overcoming the Light‐Soaking Problem in Inverted Polymer Solar Cells by Introducing a Heavily Doped Titanium Sub‐Oxide Functional Layer

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