lizhendong

Organic solar cells hold promise of providing low-cost, renewable power generation, with current devices providing up to 13% power conversion efficiency. The rational design of more performant systems requires an in-depth understanding of the interactions between the electron donating and electron accepting materials within the active layers of these devices. Here, we explore works that give insight into the intermolecular interactions between electron donors and electron acceptors, and the impact of molecular orientations and environment on these interactions. We highlight, from a theoretical standpoint, the effects of intermolecular interactions on the stability of charge carriers at the donor/acceptor interface and in the bulk and how these interactions influence the nature of the charge transfer states as well as the charge separation and charge transport processes.

An assessment of intermolecular interactions and their impact on electronic processes in organic solar cells is presented. While a great deal has been learned about the molecular-scale optical and electronic processes in these devices, a complete understanding of how the active-layer composition and morphology influence the charge transfer states, polarization and charge separation still needs to be reached.

Organic solar cells (OSCs) and organic-inorganic metal halide perovskite solar cells (pero-SCs) have been regarded as two promising photovoltaic technologies. The recent advances with power conversion efficiency over 10% and 20% have been realized in OSCs and pero-SCs, respectively. The fullerene derivatives play important role as acceptor materials in OSCs and cathode buffer layer (CBL) materials in OSCs and pero-SCs. Here, we provide a comprehensive overview of recent progresses and perspectives of the functional fullerene derivatives as acceptor materials and CBLs for OSCs and pero-SCs.

Fullerene derivatives play a very important role as acceptor materials in organic solar cells (OSCs), cathode buffer layer materials in OSCs and perovskite solar cells (pero-SCs). Here, a comprehensive overview of recent progresses and perspectives of functional fullerene derivatives as acceptor materials and buffer layer materials for OSCs and pero-SCs is provided.

All-polymer solar cells (all-PSCs) utilizing p-type polymers as electron-donors and n -typepolymers as electron-acceptors have attracted a great deal of attention, and their efficiencies have been improved considerably. Here, five polymer donors with different molecular orientations are synthesized by random copolymerization of 5-fluoro-2,1,3-benzothiadiazole with different relative amounts of 2,2′-bithiophene (2T) and dithieno[3,2-b;2′,3′-d]thiophene (DTT). Solar cells are prepared by blending the polymer donors with a naphthalene diimide-based polymer acceptor (PNDI) or a [6,6]-phenyl C₇₁-butyric acid methyl ester (PC₇₁BM) acceptor and their morphologies and crystallinity as well as optoelectronic, charge-transport and photovoltaic properties are studied. Interestingly, charge generation in the solar cells is found to show higher dependence on the crystal orientation of the donor polymer for the PNDI-based all-PSCs than for the conventional PC₇₁BM-based PSCs. As the population of face-on-oriented crystallites of the donor increased in PNDI-based PSC, the short-circuit current density (J_SC) and external quantum efficiency of the devices are found to significantly improve. Consequently, device efficiency was enhanced of all-PSC from 3.11% to 6.01%. The study reveals that producing the same crystal orientation between the polymer donor and acceptor (face-on/face-on) is important in all-PSCs because they provide efficient charge transfer at the donor/acceptor interface.

Five polymer donors showing different molecular orientations are synthesized by carrying out random copolymerization, and their photovoltaic properties are investigated by fabricating all-polymer solar cells using a PNDI polymer acceptor. As compared with PC₇₁BM-based devices, charge generation in the PNDI-based devices is found to be highly dependent on the orientation of the polymer donor.

Perovskite solar cells (PSCs) are demonstrating great potential to compete with second generation photovoltaics. Nevertheless, the key issue hindering PSCs full exploitation relies on their stability. Among the strategies devised to overcome this problem, the use of carbon nanostructures (CNSs) as hole transporting materials (HTMs) has given impressive results in terms of solar cells stability to moisture, air oxygen, and heat. Here, the use of a HTM based on a poly(3-hexylthiophene) (P3HT) matrix doped with organic functionalized single walled carbon nanotubes (SWCNTs) and reduced graphene oxide in PSCs is proposed to achieve higher power conversion efficiencies (η = 11% and 7.3%, respectively) and prolonged shelf-life stabilities (480 h) in comparison with a benchmark PSC fabricated with a bare P3HT HTM (η = 4.3% at 480 h). Further endurance test, i.e., up to 3240 h, has shown the failure of all the PSCs based on undoped P3HT, while, on the contrary, a η of ≈8.7% is still detected from devices containing 2 wt% SWCNT-doped P3HT as HTM. The increase in photovoltaic performances and stabilities of the P3HT-CNS-based solar cell, with respect to the standard P3HT-based one, is attributed to the improved interfacial contacts between the doped HTM and the adjacent layers.

Improved photovoltaic efficiencies and stabilities over prolonged times are demonstrated for perovskite solar cells based on a poly-3(hexylthiophene) layer doped with organic functionalized single-walled carbon nanotubes and reduced graphene oxide with respect to a reference device based on the undoped polymer.

Organic–inorganic lead halide perovskite materials have recently attracted much attention in the field of optoelectronic devices. Here, a hybrid piezoelectric nanogenerator based on a composite of piezoelectric formamidinium lead halide perovskite (FAPbBr₃) nanoparticles and polydimethylsiloxane polymer is fabricated. Piezoresponse force spectroscopy measurements reveal that the FAPbBr₃ nanoparticles contain well-developed ferroelectric properties with high piezoelectric charge coefficient (d₃₃) of 25 pmV⁻¹. The flexible device exhibits high performance with a maximum recordable piezoelectric output voltage of 8.5 V and current density of 3.8 μA cm⁻² under periodically vertical compression and release operations. The alternating energy generated from nanogenerators can be used to charge a capacitor and light up a red light-emitting diode through a bridge rectifier. This result innovatively expands the feasibility of organic–inorganic lead halide perovskite materials for application in a wide variety of high-performance energy harvesting devices.

The hybrid piezoelectric nanogenerators based on a composite of piezoelectric organic–inorganic lead halide perovskite materials and polydimethylsiloxane polymer are demonstrated. The recordable maximum piezoelectric output voltage and current density up to 8.5 V and 3.8 μA cm⁻² are successfully obtained under periodically vertical compression.

A ternary-blend strategy is presented to surmount the shortcomings of both fullerene derivatives and nonfullerene small molecules as acceptors for the first time. The optimal ternary device shows a high power conversion efficiency (PCE) of 10.4%. Moreover, a significant enhancement in PCE (≈35%) relative to both of the binary reference devices, which has never been achieved before in high-efficiency ternary devices, is demonstrated.

The feasibility of co-depositing a hole-conductor and a perovskite layer is demonstrated to simplify the preparation process of perovskite solar cells. The CuSCN incorporated in the perovskite layer can participate in forming the perovskite/CuSCN bulk-heterojunction and accelerate hole transport effectively, which eventually leads to a maximum power conversion efficiency of 18.1% with almost no J–V hysteresis.

Carbon nanotubes have a variety of remarkable electronic and mechanical properties that, in principle, lend them to promising optoelectronic applications. However, the field has been plagued by heterogeneity in the distributions of synthesized tubes and uncontrolled bundling, both of which have prevented nanotubes from reaching their full potential. Here, a variety of recently demonstrated solution-processing avenues is presented, which may combat these challenges through manipulation of nanoscale structures. Recent advances in polymer-wrapping of single-walled carbon nanotubes (SWNTs) are shown, along with how the resulting nanostructures can selectively disperse tubes while also exploiting the favorable properties of the polymer, such as light-harvesting ability. New methods to controllably form nanoengineered SWNT networks with controlled nanotube placement are discussed. These nanoengineered networks decrease bundling, lower the percolation threshold, and enable a strong enhancement in charge conductivity compared to random networks, making them potentially attractive for optoelectronic applications. Finally, SWNT applications, to date, in organic and perovskite photovoltaics are reviewed, and insights as to how the aforementioned recent advancements can lead to improved device performance provided.

The state of the art in functionalized single-walled carbon nanotubes (SWNTs) and conductive networks for opto-electronic applications is reviewed. An outlook on new strategies for enhancing charge extraction and transport in photovoltaic systems incorporating SWNTs is discussed, including organic photovoltaics and the new field of perovskite-based photovoltaics.

Small-molecule nonfullerene-based tandem organic solar cells (OSCs) are fabricated for the first time by utilizing P3HT:SF(DPPB)₄ and PTB7-Th:IEIC bulk heterojunctions as the front and back subcells, respectively. A power conversion efficiency of 8.48% is achieved with an ultrahigh open-circuit voltage of 1.97 V, which is the highest voltage value reported to date among efficient tandem OSCs.

The majority of hole-transporting layers used in n-i-p perovskite solar cells contain 4-tert butylpyridine (tBP). High power-conversion efficiencies and, in particular, good steady-state performance appears to be contingent on the inclusion of this additive. On the quest to improve the steady state efficiencies of the carbon nanotube-based hole-transporter system, this study has found that the presence of tBP results in an extraordinary improvement in the performance of these devices. By deconstructing a prototypical device and investigating the effect of tBP on each individual layer, the results of this study indicate that this performance enhancement must be due to a direct chemical interaction between tBP and the perovskite material. This study proposes that tBP serves to p-dope the perovskite layer and investigates this theory with poling and work function measurements.

The effect of the hole-transporter additive 4-tert Butylpyridine (tBP) on the device performance of perovskite solar cells is investigated. The additive is shown to improve the steady-state efficiency of perovskite solar cells independent of the hole-transport material. A direct interaction between tBP and the perovskite absorber is identified as being responsible for the observed improvement.

Bis(thiophen-2-yl)-diketopyrrolopyrrole (DPP) dyes bearing various alkyl substituents at the amide positions (n-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, 2-ethylhexyl) and chlorine (Cl), bromine (Br), or cyano (CN) substituents at the thiophene positions have been synthesized and investigated with regard to their molecular and semiconducting properties. Intense absorption, strong fluorescence, and reversible oxidation and reduction processes are common to all of these dyes. Their characterization as organic semiconductors in vacuum-processed thin-film transistors reveals p-channel operation with field-effect mobilities ranging from 0.01 to 0.7 cm² V⁻¹ s⁻¹. The highest mobility is found for the DPP dyes bearing the 2-ethylhexyl substituents, which is surprising, considering that as a result of the chiral substituents, this material is a mixture of (R,R), (S,S), and (R,S) stereoisomers. The high carrier mobility in the films of the DPPs bearing stereoisomerically inhomogeneous ethylhexyl groups is rationalized here by single-crystal X-ray diffraction (XRD) analysis in combination with XRD and atomic force microscopy studies on thin films, which reveal the presence of slightly different 2D layer arrangements for the n-alkyl and the 2-ethylhexyl derivatives. For the cyano-substituted DPPs possessing the lowest LUMO levels, ambipolar transport characteristics are observed.

Twenty-four diketopyrrolopyrrole dyes with branched and linear solubilizing alkyl chains and electron-withdrawing substituents at the aromatic core are investigated as the semiconductor in organic thin-film transistors. Remarkably, layers of stereoisomeric mixtures of the 2-ethylhexyl-substituted derivatives outperform the devices of dyes with n-alkyl chains with carrier mobilities as high as 0.7 cm² V⁻¹ s⁻¹.

Fine energy-level modulations of small-molecule acceptors (SMAs) are realized via subtle chemical modifications on strong electron-withdrawing end-groups. The two new SMAs (IT-M and IT-DM) end-capped by methyl-modified dicycanovinylindan-1-one exhibit upshifted lowest unoccupied molecular orbital (LUMO) levels, and hence higher open-circuit voltages can be observed in the corresponding devices. Finally, a top power conversion efficiency of 12.05% is achieved.

A highly efficient fullerene-free polymer solar cell (PSC) based on PDCBT, a polythiophene derivative substituted with alkoxycarbonyl, achieves an impressive power conversion efficiency of 10.16%, which is the best result in PSCs based on polythiophene derivatives to date. In comparison with a poly(3-hexylthiophene):ITIC-based device, the photovoltaic and morphological properties of the PDCBT:ITIC-based device are carefully investigated and interpreted.