Search

Photo-induced electron transfer between poly-(3-hexylthiophene) (P3HT) and small (2.4 nm) PbS quantum dots (QDs), capped by different ligands, was studied by picosecond and femtosecond time-resolved fluorescence and by photo-induced absorption (PIA) measurements. In line with previous experiments, we observed that the efficiency of the quenching of P3HT by PbS QDs increased upon decreasing the average thickness of the ligand shell. This trend was also observed in the PIA spectra and in prior work on the performance of photovoltaic devices where the active layer was a blend of P3HT with PbS QDs capped by different ligands. Combining the pico- and femtosecond fluorescence decays showed that the quenching in blend films of P3HT and PbS QDs treated with 1,4-benzenedithiol occurred over a broad time scale ranging from tens of femtoseconds to hundreds of picoseconds. This complex kinetics was attributed to exciton hopping followed by electron transfer to the conduction band of the QDs. We also compared the wavelength dependence of the internal quantum efficiency (IQE) in the hybrid photovoltaic devices to those devices where the photoactive layer consists of PbS QDs only. Although excitation in the first excitonic transition of the PbS QDs yielded a similar IQE in both devices, the IQE of the hybrid devices tripled at wavelengths where also P3HT started to absorb. This suggests that upon excitation of P3HT in the latter devices, charge generation occurs by photo-induced electron transfer from P3HT to the QDs rather than by energy transfer to the QDs followed by exciton dissociation in the QDs. [ABSTRACT FROM AUTHOR]

Different approaches of surface modification of the quantum dots (QDs), namely, solution-phase (octylamine, octanethiol) and post-deposition (acetic acid, 1,4-benzenedithiol) ligand exchange were used in the fabrication of hybrid bulk heterojunction solar cell containing poly (3-hexylthiophene) (P3HT) and small (2.4 nm) PbS QDs. We show that replacing oleic acid by shorter chain ligands improves the figures of merit of the solar cells. This can possibly be attributed to a combination of a reduced thickness of the barrier for electron transfer and an optimized phase separation. The best results were obtained for post-deposition ligand exchange by 1,4-benzenedithiol, which improves the power conversion efficiency of solar cells based on a bulk heterojunction of lead sulfide (PbS) QDs and P3HT up to two orders of magnitude over previously reported hybrid cells based on a bulk heterojunction of P3HT:PbS QDs, where the QDs are capped by acetic acid ligands. The optimal performance was obtained for solar cells with 69 wt.% PbS QDs. Besides the ligand effects, the improvement was attributed to the formation of an energetically favorable bulk heterojunction with P3HT, when small size (2.4 nm) PbS QDs were used. Dark current density-voltage (J-V) measurements carried out on the device provided insight into the working mechanism: the comparison between the dark J-V characteristics of the bench mark system P3HT:PCBM and the P3HT:PbS blends allows us to conclude that a larger leakage current and a more efficient recombination are the major factors responsible for the larger losses in the hybrid system. [ABSTRACT FROM AUTHOR]

Solution‐processed metal oxide thin‐film transistors (TFTs) represent a promising technology for applications in existing but also emerging large‐area electronics. However, high process temperatures and lengthy annealing times represent two remaining technical challenges. Different approaches aiming to address these challenges have been proposed but progress remains modest. Here, the development of high electron mobility metal oxide TFTs based on photonically converted Al2O3/ZrO2 and In2O3/ZnO bilayers acting as the high‐k dielectric and electron‐transporting channel, respectively is described. Sequential solution‐phase deposition and photonic processing lead to low substrate temperature (<200 °C) while minimizing the overall process time to less than 60 s without compromising the quality of the formed layers. The bilayer Al2O3/ZrO2 dielectric exhibits low leakage current density (10−6 A cm−2 at 1 MV cm−1), high geometric capacitance (≈120 nF cm−2) and breakdown electric field of ≈1 MV cm−1. Combining Al2O3/ZrO2 with a photonically converted In2O3/ZnO heterojunction channels, results in TFTs with high electron mobility (19 cm2 V−1 s−1), low operation voltage (≤2 V), high current on/off ratio (>106), and low subthreshold swing (108 mV dec−1), that can be manufactured even onto thermally sensitive polymer substrates. The work is a significant step toward all‐photonic processed metal oxide electronics. [ABSTRACT FROM AUTHOR]

Poly(isoindigo- alt-3,4-difluorothiophene) (PIID[2F]T) analogues used as 'polymer acceptors' in bulk-heterojunction (BHJ) solar cells achieve >7 % efficiency when used in conjunction with the polymer donor PBFTAZ (model system; copolymer of benzo[1,2- b:4,5- b′]dithiophene and 5,6-difluorobenzotriazole). Considering that most efficient polymer-acceptor alternatives to fullerenes (e.g. PC61BM or its C71 derivative) are based on perylenediimide or naphthalenediimide motifs thus far, branched alkyl-substituted PIID[2F]T polymers are particularly promising non-fullerene candidates for 'all-polymer' BHJ solar cells. [ABSTRACT FROM AUTHOR]

'Nonfullerene' acceptors are proving effective in bulk heterojunction (BHJ) solar cells when paired with selected polymer donors. However, the principles that guide the selection of adequate polymer donors for high-efficiency BHJ solar cells with nonfullerene acceptors remain a matter of some debate and, while polymer main-chain substitutions may have a direct influence on the donor-acceptor interplay, those effects should be examined and correlated with BHJ device performance patterns. This report examines a set of wide-bandgap polymer donor analogues composed of benzo[1,2- b:4,5- b′]dithiophene (BDT), and thienyl ([2H]T) or 3,4-difluorothiophene ([2F]T) motifs, and their BHJ device performance pattern with the nonfullerene acceptor 'ITIC'. Studies show that the fluorine- and ring-substituted derivative PBDT(T)[2F]T largely outperforms its other two polymer donor counterparts, reaching power conversion efficiencies as high as 9.8%. Combining several characterization techniques, the gradual device performance improvements observed on swapping PBDT[2H]T for PBDT[2F]T, and then for PBDT(T)[2F]T, are found to result from (i) notably improved charge generation and collection efficiencies (estimated as ≈60%, 80%, and 90%, respectively), and (ii) reduced geminate recombination (being suppressed from ≈30%, 25% to 10%) and bimolecular recombination (inferred from recombination rate constant comparisons). These examinations will have broader implications for further studies on the optimization of BHJ solar cell efficiencies with polymer donors and a wider range of nonfullerene acceptors. [ABSTRACT FROM AUTHOR]

Simple and low-cost two-dimensional (2D) materials are of great interest considering their wide use in various device applications. Here, we present the application of 2D materials, i.e., graphene oxide (GO), molybdenum disulfide (MoS 2), and tungsten disulfide (WS 2) as hole transport layer (HTL) in non-fullerene acceptors (NFAs) organic photovoltaics (OPVs) using device simulation. The numerical simulation was carried out using SCAPS-1D and specifically focused on the effect of thickness and defect density at the active layer on the photovoltaic characteristics of the devices. In addition, the influence of defect density at the HTL/active layer interface on the device performance was also studied. After conducting a series of optimization, an optimum power conversion efficiency (PCE) of 15.89%, 20.05%, and 23.55% was achieved for NFA-based OPV with GO, MoS 2 , and WS 2 , respectively. This work provides a practical explanation of the feasible performance enhancement and critical design parameters for OPV devices. The results showcase the potential application of 2D materials as low-cost HTL for high-efficiency organic solar cells. [Display omitted] • Device modelling 2D – HTM of non-fullerene acceptor organic photovoltaic was comprehensively performed. • The influence of physical parameters on NFA – OPVs performance was thoroughly discussed. • After optimization, we obtained PCE of 15.89%, 20.05%, and 23.55% for GO, MoS 2 , and WS 2 as HTM, respectively. • The study promotes future OPVs optimization and performance enhancement. [ABSTRACT FROM AUTHOR]

Large‐scale production of organic solar modules requires low‐cost and reliable materials with reproducible batch‐to‐batch properties. In case of polymers, their (photo)physical properties depend strongly on the polymers' molecular weight (MW). Herein, the impact of the MW of the donor polymer poly(3‐hexylthiophene) (P3HT) on the photophysics is studied in blends with a recently developed rhodanine‐endcapped indacenodithiophene nonfullerene acceptor (IDTBR), a bulk heterojunction (BHJ) system that potentially fulfills the aforementioned criteria for large‐scale production. It is found that the power conversion efficiency (PCE) increases when the weight‐average MW is increased from 17 kDa (PCE: 4.0%) to 34 kDa (PCE: 6.6%), whereas a further increase in MW leads to a reduced PCE of 4.4%. It is demonstrated that the charge generation efficiency, as estimated from time‐delayed collection field experiments, varies with the P3HT MW and is the reason for the differences in photocurrent and device performance. These findings provide insight into the fundamental photophysical reasons of the MW dependence of the PCE, which is taken into account when using polymer‐based nonfullerene acceptor blends in solar cell devices and modules. [ABSTRACT FROM AUTHOR]