Electron-donating amine-interlayer induced n-type doping of polymer:nonfullerene blends for efficient narrowband near-infrared photo-detection.

Inherently narrowband near-infrared organic photodetectors are highly desired for many applications, including biological imaging and surveillance. However, they suffer from a low photon-to-charge conversion efficiencies and utilize spectral narrowing techniques which strongly rely on the used material or on a nano-photonic device architecture. Here, we demonstrate a general and facile approach towards wavelength-selective near-infrared phtotodetection through intentionally n-doping 500-600 nm-thick nonfullerene blends. We show that an electron-donating amine-interlayer can induce n-doping, resulting in a localized electric field near the anode and selective collection of photo-generated carriers in this region. As only weakly absorbed photons reach this region, the devices have a narrowband response at wavelengths close to the absorption onset of the blends with a high spectral rejection ratio. These spectrally selective photodetectors exhibit zero-bias external quantum efficiencies of ~20-30% at wavelengths of 900-1100 nm, with a full-width-at-half-maximum of ≤50 nm, as well as detectivities of >1012 Jones.

Robust metal ion-chelated polymer interfacial layer for ultraflexible non-fullerene organic solar cells.

Achieving high power conversion efficiency and good mechanical robustness is still challenging for the ultraflexible organic solar cells. Interlayers simultaneously having good mechanical robustness and good chemical compatibility with the active layer are highly desirable. In this work, we present an interlayer of Zn2+-chelated polyethylenimine (denoted as PEI-Zn), which can endure a maximum bending strain over twice as high as that of ZnO and is chemically compatible with the recently emerging efficient nonfullerene active layers. On 1.3 µm polyethylene naphthalate substrates, ultraflexible nonfullerene solar cells with the PEI-Zn interlayer display a power conversion efficiency of 12.3% on PEDOT:PSS electrodes and 15.0% on AgNWs electrodes. Furthermore, the ultraflexible cells show nearly unchanged power conversion efficiency during 100 continuous compression-flat deformation cycles with a compression ratio of 45%. At the end, the ultraflexible cell is demonstrated to be attached onto the finger joint and displays reversible current output during the finger bending-spreading.

Flexible All-Solution-Processed Organic Solar Cells with High-Performance Nonfullerene Active Layers.

All-solution-processed organic solar cells (from the bottom substrate to the top electrode) are highly desirable for low-cost and ubiquitous applications. However, it is still challenging to fabricate efficient all-solution-processed organic solar cells with a high-performance nonfullerene (NF) active layer. Issues of charge extraction and wetting are persistent at the interface between the nonfullerene active layer and the printable top electrode (PEDOT:PSS). In this work, efficient all-solution-processed NF organic solar cells (from the bottom substrate to the top electrode) are reported via the adoption of a layer of hydrogen molybdenum bronze (HX MoO3 ) between the active layer and the PEDOT:PSS. The dual functions of HX MoO3 include: 1) its deep Fermi level of -5.44 eV can effectively extract holes from the active layer; and 2) the wetting issues of the PEDOT:PSS on the hydrophobic surface of the NF active layer can be solved. Importantly, fine control of the HX MoO3 composition during the synthesis is critical in obtaining processing orthogonality between HX MoO3 and the PEDOT:PSS. Flexible all-solution-processed NF organic solar cells with power conversion efficiencies of 11.9% and 10.3% are obtained for solar cells with an area of 0.04 and 1 cm2 , respectively.

Exploring the Chemical Interaction between Diiodooctane and PEDOT-PSS Electrode for Metal Electrode-Free Nonfullerene Organic Solar Cells.

Metal electrode-free organic solar cells with a printable top electrode are attractive in realizing the low cost of photovoltaics. Interaction between the printable electrode and the active layer is critical to the device performance. In this work, we report the chemical interaction between the printable polymer electrode poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and the typically used additive of 1,8-dioodooctane (DIO) in the active layer. DIO can be converted to hydrogen iodide (HI) under the acidic condition of PEDOT:PSS, and the HI chemically reduces the PEDOT:PSS with the appearance of an absorbance band at 800-1100 nm. The generation of I2 is verified by the color change of starch. The reaction results in a decrease of its work function that hinders efficient hole collection. A strategy is proposed to circumvent the detrimental interaction by inserting an ultrathin (15 nm) active layer without DIO between the initial active layer and the PEDOT:PSS electrode. A power conversion efficiency of 10.1% is achieved for the metal electrode-free nonfullerene organic solar cells.

Tailoring vertical phase distribution of quasi-two-dimensional perovskite films via surface modification of hole-transporting layer.

Vertical phase distribution plays an important role in the quasi-two-dimensional perovskite solar cells. So far, the driving force and how to tailor the vertical distribution of layer numbers have been not discussed. In this work, we report that the vertical distribution of layer numbers in the quasi-two-dimensional perovskite films deposited on a hole-transporting layer is different from that on glass substrate. The vertical distribution could be explained by the sedimentation equilibrium because of the colloidal feature of the perovskite precursors. Acid addition will change the precursors from colloid to solution that therefore changes the vertical distribution. A self-assembly layer is used to modify the acidic surface property of the hole-transporting layer that induces the appearance of desired vertical distribution for charge transport. The quasi-two-dimensional perovskite cells with the surface modification display a higher open-circuit voltage and a higher efficiency comparing to reference quasi-two-dimensional cells.

A low-temperature carbon electrode with good perovskite compatibility and high flexibility in carbon based perovskite solar cells.

A low-temperature carbon electrode with good perovskite compatibility is employed in hole-transport-material free perovskite solar cells, and a champion power conversion efficiency (PCE) of 11.7% is obtained. The PCE is enhanced to 14.55% by an interface modification of PEDOT:PSS. The application of this carbon on ITO/PEN substrates is also demonstrated.

Suppressing generation of iodine impurity via an amidine additive in perovskite solar cells.

In perovskite solar cells, I- tends to oxidize to I2 due to its low redox potential. The generated I2 has been proved to be detrimental to device performance. Herein, for the first time, an amidine DBU is introduced as an additive into the precursor of the perovskite layer. The reductive DBU can suppress the formation of iodine impurity, resulting in a highly pure perovskite polycrystalline film. The efficiency and stability of the perovskite solar cells are thus improved.