Reducing nonradiative recombination is crucial for minimizing voltage losses in metal-halide perovskite solar cells and achieving high power conversion efficiencies. Photoluminescence spectroscopy on complete or partial perovskite solar cell stacks is often used to quantify and disentangle bulk and interface contributions to nonradiative losses. Accurately determining the intrinsic loss in a perovskite layer is key to analyzing the origins of nonradiative recombination and developing defect engineering strategies.
View Article and Find Full Text PDFAll-perovskite tandem photovoltaics are a potentially cost-effective technology to power chemical fuel production, such as green hydrogen. However, their application is limited by deficits in open-circuit voltage and, more challengingly, poor operational stability of the photovoltaic cell. Here we report a laboratory-scale solar-assisted water-splitting system using an electrochemical flow cell and an all-perovskite tandem solar cell.
View Article and Find Full Text PDFIn p-i-n perovskite solar cells optical excitation of defect states at the interface between the perovskite and fullerene electron transport layer (ETL) creates a photocurrent responsible for a distinct sub-bandgap external quantum efficiency (EQE). The precise nature of these signals and their impact on cell performance are largely unknown. Here, the effect of n-doping the fullerene on the EQE spectra is studied.
View Article and Find Full Text PDFThe short exciton diffusion length in organic semiconductors results in a strong dependence of the conversion efficiency of organic photovoltaic (OPV) cells on the morphology of the donor-acceptor bulk-heterojunction blend. Strong light-matter coupling provides a way to circumvent this dependence by combining the favorable properties of light and matter via the formation of hybrid exciton-polaritons. By strongly coupling excitons in P3HT-C OPV cells to Fabry-Perot optical cavity modes, exciton-polaritons are formed with increased propagation lengths.
View Article and Find Full Text PDFThe efficiency of perovskite solar cells is affected by open-circuit voltage losses due to radiative and non-radiative charge recombination. When estimated using sensitive photocurrent measurements that cover the above- and sub-bandgap regions, the radiative open-circuit voltage is often unphysically low. Here we report sensitive photocurrent and electroluminescence spectroscopy to probe radiative recombination at sub-bandgap defects in wide-bandgap mixed-halide lead perovskite solar cells.
View Article and Find Full Text PDFCrystallization of low-dimensional perovskites is a complex process that leads to multidimensional films comprising two-dimensional (2D), quasi-2D, and three-dimensional (3D) phases. Most quasi-2D perovskite films possess a regular gradient with 2D phases located at the bottom of the film and 3D phases at the top. Recently, multiple studies have reported reverse-graded perovskite films, where the location of the 2D and 3D structures is inverted.
View Article and Find Full Text PDFPhotoinduced halide segregation hinders widespread application of three-dimensional (3D) mixed-halide perovskites. Much less is known about this phenomenon in lower-dimensional systems. Here, we study photoinduced halide segregation in lower-dimensional mixed iodide-bromide perovskites (PEAMA Pb (Br I ), with PEA: phenethylammonium and MA: methylammonium) through time-dependent photoluminescence (PL) spectroscopy.
View Article and Find Full Text PDF2H-Benzotriazol-2-ylethylammonium bromide and iodide and its difluorinated derivatives are synthesized and employed as interlayers for passivation of formamidinium lead triiodide (FAPbI) solar cells. In combination with PbI and PbBr, these benzotriazole derivatives form two-dimensional (2D) Ruddlesden-Popper perovskites (RPPs) as evidenced by their crystal structures and thin film characteristics. When used to passivate n-i-p FAPbI solar cells, the power conversion efficiency improves from 20% to close to 22% by enhancing the open-circuit voltage.
View Article and Find Full Text PDFCreating new donor materials is crucial for further advancing organic solar cells. Random terpolymers have been adopted to overcome shortcomings of regular alternating donor-acceptor (D-A) polymers of which the performance is often susceptible to batch-to-batch variations. In general, the properties and performance of efficient D -A-D -A and D-A -D-A terpolymers are sensitive to the D /D or A /A monomer ratios.
View Article and Find Full Text PDFLow-dimensional perovskites attract increasing interest due to tunable optoelectronic properties and high stability. Here, it is shown that perovskite thin films with a vertical gradient in dimensionality result in graded electronic bandgap structures that are ideal for photodiode applications. Positioning low-dimensional, vertically-oriented perovskite phases at the interface with the electron blocking layer increases the activation energy for thermal charge generation and thereby effectively lowers the dark current density to a record-low value of 5 × 10 mA cm without compromising responsivity, resulting in a noise-current-based specific detectivity exceeding 7 × 10 Jones at 600 nm.
View Article and Find Full Text PDFAn efficient substrate-configuration p-i-n metal-halide perovskite solar cell (PSC) is fabricated on a polymer-coated steel substrate. The optimized cell employs a Ti bottom electrode coated with a thin indium tin oxide (ITO) interlayer covered with a self-assembled [2-(9-carbazol-9-yl)ethyl]phosphonic acid monolayer as a hole-selective contact. A triple-cation perovskite is used as the absorber layer.
View Article and Find Full Text PDFACS Appl Mater Interfaces
April 2022
Interface layers used for electron transport (ETL) and hole transport (HTL) often significantly enhance the performance of organic solar cells (OSCs). Surprisingly, interface engineering for hole extraction has received little attention thus far. By finetuning the chemical structure of carbazole-based self-assembled monolayers with phosphonic acid anchoring groups, varying the length of the alkane linker (2PACz, 3PACz, and 4PACz), these HTLs were found to perform favorably in OSCs.
View Article and Find Full Text PDFDefects in perovskite solar cells are known to affect the performance, but their precise nature, location, and role remain to be firmly established. Here, we present highly sensitive measurements of the sub-bandgap photocurrent to investigate defect states in perovskite solar cells. At least two defect states can be identified in p-i-n perovskite solar cells that employ a polytriarylamine hole transport layer and a fullerene electron transport layer.
View Article and Find Full Text PDFPerovskite-based multijunction solar cells are a potentially cost-effective technology that can help surpass the efficiency limits of single-junction devices. However, both mixed-halide wide-bandgap perovskites and lead-tin narrow-bandgap perovskites suffer from non-radiative recombination due to the formation of bulk traps and interfacial recombination centers which limit the open-circuit voltage of sub-cells and consequently of the integrated tandem. Additionally, the complex optical stack in a multijunction solar cell can lead to losses stemming from parasitic absorption and reflection of incident light which aggravates the current mismatch between sub-cells, thereby limiting the short-circuit current density of the tandem.
View Article and Find Full Text PDFLight-induced halide segregation hampers obtaining stable wide-band-gap solar cells based on mixed iodide-bromide perovskites. So far, the effect of prolonged illumination on the performance of mixed-halide perovskite solar cells has not been studied in detail. It is often assumed that halide segregation leads to a loss of open-circuit voltage.
View Article and Find Full Text PDFFew semiconducting polymers are known that possess more than one semi-crystalline structure. Guidelines for rationalizing or creating polymorphism in these materials do not exist. Two different semi-crystalline polymorphs, and , and an amorphous phase have recently been identified for alternating diketopyrrolopyrrole-quaterthiophene copolymers (PDPP4T).
View Article and Find Full Text PDFParasitic optical absorption is one of the root causes of the moderate efficiency of metal halide perovskite solar cells (PSCs) with an opaque substrate configuration. Here, we investigate the reduction of these optical losses by using thin (7-10 nm), undoped, thermally evaporated 2,2',7,7'-tetrakis[,-di(4-methoxyphenyl)amino]-9,9'-spirobifluorene (spiro-OMeTAD), ,'-di(1-naphthyl)-,'-diphenyl-(1,1'-biphenyl)-4,4'-diamine) (NPB), and tris(4-carbazoyl-9-ylphenyl)amine) (TCTA) hole transport layers (HTLs). Of these, NPB is found to offer the best compromise between efficiency and stability.
View Article and Find Full Text PDFThe combination of narrow-bandgap diketopyrrolopyrrole (DPP) polymers and nonfullerene acceptors (NFAs) seems well-matched for solar cells that exclusively absorb in the near infrared but they rarely provide high efficiency. One reason is that processing of the active layer is complicated by the fact that DPP-based polymers are generally only sufficiently soluble in chloroform (CF), while NFAs are preferably processed from halogenated aromatic solvents. By using a ternary solvent system consisting of CF, 1,8-diiodooctane (DIO), and chlorobenzene (CB), the short-circuit current density is increased by 50% in solar cells based on a DPP polymer (PDPP5T) and a NFA (IEICO-4F) compared to the use of CF with DIO only.
View Article and Find Full Text PDFElectron transport layers (ETLs) placed between the electrodes and a photoactive layer can enhance the performance of organic solar cells but also impose limitations. Most ETLs are ultrathin films, and their deposition can disturb the morphology of the photoactive layers, complicate device fabrication, raise cost, and also affect device stability. To fully overcome such drawbacks, efficient organic solar cells that operate without an ETL are preferred.
View Article and Find Full Text PDFJ Phys Chem C Nanomater Interfaces
December 2020
The effect of the nature of the π-conjugated linker that is positioned between electron-deficient 2,5-dihydropyrrolo[3,4-]pyrrole-1,4-dione (DPP) and electron-rich dithieno[3,2-:2',3'-]pyrrole (DTP) units in alternating DPP-DTP copolymers on the optical and electrochemical band gaps and the effective exciton binding energy is investigated for six different aromatic linkers. The optical band gap is related to the electron-donating properties of DTP and the electron-withdrawing properties of DPP but likewise strongly affected by the nature of the linker and varies between 1.13 and 1.
View Article and Find Full Text PDFJ Phys Chem C Nanomater Interfaces
November 2020
The optical properties of two sets of donor-acceptor-donor molecules with terminal bithiophene donor units and a central diketopyrrolopyrrole (DPP) acceptor unit are studied. The two sets differ in the alkyl chains on the DPP, which are either branched at the α-carbon (3-pentyl) (-) or linear (-hexyl) (-). Within each set, the molecules differ by the absence or presence of -hexyl chains on the terminal thiophene rings in the 3', 4', or 5' positions.
View Article and Find Full Text PDFPerovskite semiconductors hold a unique promise in developing multijunction solar cells with high-efficiency and low-cost. Besides design constraints to reduce optical and electrical losses, integrating several very different perovskite absorber layers in a multijunction cell imposes a great processing challenge. Here, we report a versatile two-step solution process for high-quality 1.
View Article and Find Full Text PDFTwo asymmetric thiophene (T)/pyridine (Py) flanked diketopyrrolopyrrole (DPP) polymers with a regiorandom and regioregular conjugated backbone are synthesized via a Stille polycondensation to investigate the effect of regioregularity on their optoelectronic properties and photovoltaic performance in fullerene-based polymer solar cells. Surprisingly, both polymers possess very similar optical bandgap, energy levels, and photovoltaic performance. These findings, combined with a factor of 19 reactivity difference between the two end groups of the asymmetric DPP monomer, intuitively suggest the formation of regular chain segments in the random polymer.
View Article and Find Full Text PDFPhotovoltaic devices that switch color depending on illumination conditions may find application in future smart window applications. Here a photochromic diarylethene molecule is used as sensitizer in a ternary bulk heterojunction blend, employing poly(4-butylphenyldiphenylamine) (poly-TPD) and [6,6]-phenyl-C-butyric acid methyl ester (PCBM) for the transport of holes and electrons, respectively. Sandwiched between two electrodes, the blend creates a photochromic photovoltaic device that changes color, light absorption, and photon-to-electron conversion efficiency in the visible spectral range after having been illuminated with UV light.
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