https://onlinelibrary.wiley.com/doi/pdf/10.1002/eom2.12127

Inorganic top electron transport layer for high performance inverted perovskite solar cells

Owing to their unique porosity and large surface area, porous organic polymers (POPs) have shown their presence in numerous novel applications. The tunability and functionality of both the pores and backbone of the material enable its suitability in photovoltaic devices. The porosity induced host-guest configurations as well as periodic donor-acceptor structures benefit the charge separation and charge transfer in photophysical processes. The role of POPS in other critical device components, such as hole transporting layers and electrodes, has also been demonstrated. Herein, this review will primarily focus on the recent progress made in applying POPs for solar cell device performance enhancement, covering organic solar cells, perovskite solar cells, and dye-sensitized solar cells. Based on the efforts in recent years in unraveling POP's photophysical process and its relevance with device performances, an in-depth analysis will be provided to address the gradual shift of attention from an entirely POP-based active layer to other device functional components. Combining the insights from device physics, material synthesis, and microfabrication, we aim to unfold the fundamental limitations and challenges of POPs and shed light on future research directions.

Porous organic polymers in solar cells.

The bandgap-dependent performance of covalent organic nanosheets (CONs) as sodium-ion battery anode materials was probed by inclusion of electron-deficient benzothiadiazole (BT) units into their network. Conjugation of BT units with electron-rich moieties afforded low-bandgap materials, and a self-assembled CON morphology with a large number of insertion sites for Na+ ions was realized via solvothermal Stille cross-coupling. The bandgap dependence of Na+ storage capacity was probed by the synthesis and characterization of large-bandgap CONs, which were subsequently compared to low-bandgap CONs in terms of electrochemical behavior. Four different CONs were investigated in total to reveal that the Na+ storage capacity can be improved by increasing the charge carrier conductivity via the inclusion of BT units, while the surface area can be controlled by maintaining the material backbone. The electrode with a solvothermally prepared low-bandgap CON demonstrated stable rate capability and cycling performance while exhibiting highly enhanced reversible discharge capacity (∼450 mA h g−1) after 30 cycles at a scan rate of 100 mA g−1. To the best of our knowledge, this discharge capacity is among the best values reported so far for organic electrodes prepared without thermal treatment.

Molecular engineering of covalent organic nanosheets for high-performance sodium-ion batteries

Although the power conversion efficiencies (PCEs) of perovskite solar cells (PSCs) have made great progress, the surface and interface defects still affect their PCE and stability and hinder the commercialization. To overcome this problem, 1-methylimidazole (1-MIm) and 1-methylbenzimidazole (1-MBIm) are used as the interfacial passivation agents to passivate the defects at surface and interface. The results indicate that, in contrast with 1-MIm, 1-MBIm displays a stronger Lewis coordination interaction with the uncoordinated Pb2+ to reduce the non-radiative recombination and also effectively improves the charge transfer capacity of perovskite films due to its strong π-π conjugate interaction, resulting in the more excellent photovoltaic performance. As a result, the PCE of the champion 1-MBIm PSC has been improved from 19.48% (pristine) to 21.22% with a dramatically enhanced open-circuit voltage (Voc=1.15 V). More importantly, a significantly improvement in long-term stability was achieved for 1-MBIm perovskite devices, which was attributed to the high-quality perovskite film caused by the strong passivation effect of 1-MBIm and the hydrogen bond with water molecules. The results offers an efficient and facile strategy by interface engineering to fabricate high-performance and stable PSCs for commercial application.

Effective Interface Defect Passivation via Employing 1-Methylbenzimidazole for Highly Efficient and Stable Perovskite Solar Cells.

Polyvinyl carbazole (P0)-based pendant polymers were synthesized by modifying carbazole motifs with pyrene derivatives (P1 and P4) to manipulate the bandgap and frontier orbital energy levels. To establish the electronic properties of pendant polymers according to structural differences, the polymers were utilized as additional hole transport layers in planar-type perovskite solar cells and organic photovoltaic cells. When P4 with thiophene-pyrene pendant was used as hole transport layer, all device parameters, except open-circuit voltage, were significantly improved in comparison with P0 and P1 (conjugated with t-butyl pyrene derivatives). Since P4 had more electrically conductive thiophene units than benzene units with fewer alkyl groups, the supramolecular assembly of P4 was found to be more favorable in electronic devices. Furthermore, devices with P4 demonstrated lower dark current than others, which could potentially be useful for charge carrier transport and sensitive photo detecting devices.

Versatile Pendant Polymer for Selective Charge Carrier Transport via Controlling the Supramolecular Self-Assembly

An electron-rich fused indoloindole-based poly(indoloindole-selenophene vinylene selenophene) was synthesized and characterized. Soxhlet can be obtained by continuously purifying the product with a specific solvent and obtaining a pure polymer with a high concentration. Molecular weight is affected by the vapor pressure of marginal solvent, and the polymer was fractionated using tetrahydrofuran, chloroform, and chlorobenzene. Solubility is closely related to the morphology of bulk heterojunction and device parameters. In the solution process of fabricating the organic solar cell, securement of solubility has a great effect on the performance of the device, because morphology and orientation of a photo-active layer which significantly affect charge transport in the device. Since tetrahydrofuran (THF) Soxhlet solvents have high vapor pressure and appropriate solubility parameters, THF induced the best solubility of P-IDI-SVS materials for organic solvents. And through additive optimization, the performance of the device based on P-IDI-SVS from THF-Soxhlet extraction was enhanced. This is expected to be a meaningful study because the effect on solubility of Soxhlet solvent suggests factors to be considered in the solution process in organic solar cell research. In addition, surface modified bulk heterojunction was observed using atomic force microscopy, photoluminescence, time-correlated single photon counting and Raman spectroscopy analysis.

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Selective Soxhlets extraction to enhance solubility of newly-synthesized poly(indoloindole-selenophene vinylene selenophene) donor for photovoltaic applications.

Solution-processable porous organic polymer for tailoring the charge transport property of planar perovskite solar cells

Among small molecule organic materials, tris(4-(1-phenyl-1H-benzo[d]imidazole)phenyl)phosphine oxide (TIPO) and 2,4,6-tris(4-(1-phenyl-1H-benzo[d]imidazol)phenyl)-1,3,5-triazine were newly synthesised and introduced into an n-type interlayer in planar perovskite solar cells for effective electron transport. The small molecule materials contain phenyl benzimidazole, which is combined with a phosphine oxide core or a triazine ring core and contributes to the improvement of charge extraction and stability. As the constituent molecules—phosphine oxide and benzimidazole—have strong polarity properties and π-electrons, the molecules induce passivating defects towards improving charge transport and flattening the surface morphology. Moreover, the stability of the device was increased due to the introduction of the TIPO material as the passivation and protection layer. In this electron extraction analysis, electrical resistance and surface morphology investigations were carried out via space charge-limited current, photoluminescence, impedance, and atomic force microscopy analyses.

Tris(4-(1-phenyl-1H-benzo[d]imidazole)phenyl)phosphine oxide for Enhanced Mobility and Restricted Traps in Photovoltaic Interlayers

In this study, a new type of low-bandgap small molecule has been synthesized with a thieno[3,4-c]pyrrole-4,6-dione (TPD) derivative for application in bulk heterojunction (BJH) solar cells. The series of solar cells were fabricated by blending the TPD-based small molecule (M1) and [6,6]-phenyl C71 butyric acid methyl ester (PC71BM). In order to optimize the performance of solar cells, the nanoscale morphologies of the BHJ layers were controlled via processing additives with 1,8-diiodooctane (DIO) and 1-chloronaphthalene (CN). Therefore, we demonstrated that the use of CN successively suppressed molecular aggregation and demonstrated suitable phase separation, in addition to increasing the power conversion efficiency from 0.36% to 1.86%.

Facile Synthetic Route of a Solution-Processable, Thieno[3,4-c]pyrrolo-4,6-dione-Based Conjugated Small Molecule and Control of the Optoelectronic Properties via Processing Additives

Jihyun Lim

Papers

Selective Soxhlets extraction to enhance solubility of newly-synthesized poly(indoloindole-selenophene vinylene selenophene) donor for photovoltaic applications.

Versatile Pendant Polymer for Selective Charge Carrier Transport via Controlling the Supramolecular Self-Assembly

Solution-processable porous organic polymer for tailoring the charge transport property of planar perovskite solar cells

Tris(4-(1-phenyl-1H-benzo[d]imidazole)phenyl)phosphine oxide for Enhanced Mobility and Restricted Traps in Photovoltaic Interlayers

Facile Synthetic Route of a Solution-Processable, Thieno[3,4-c]pyrrolo-4,6-dione-Based Conjugated Small Molecule and Control of the Optoelectronic Properties via Processing Additives