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This work reveals the relationships between the ion species and charge collection, and enhances both the efficiency and stability of a PSC device.

In early studies on organic solar cells with high conductivity PEDOT:PSS, the contact between ITO and PEDOT:PSS was considered ohmic. However, because low-conductivity PEDOT:PSS (such as AI4083) is mainly utilized in contemporary solar cells, the contact between ITO and PEDOT:PSS is not ohmic anymore. Despite the high possibility that there are serious interface problems, little attention has been paid to the interface between PEDOT:PSS and ITO. Most of the previous studies of interfaces in organic solar cells have focused on the interface between the active and charge transport layers. In this work, we have employed a conjugated polyelectrolyte that uses potassium poly[9,9-bis(3′-sulfonatopropyl)fluorene-alt-(9-(2,7-diethylheptyl)-carboazole)] (WPFSCz-) between ITO and low-conductivity PEDOT:PSS to overcome complicated organic–inorganic interfacial problems. The insertion of the WPFSCz- layer provides substantial advantages in the operation of polymer solar cells. First, the inserted WPFSCz- layer modifies the work-function of ITO, thereby forming an effective cascading energy alignment, which is favorable for good hole transport. Second, the introduction of the WPFSCz- layer eliminates interfacial trap sites. The reduction in traps reduces recombination losses at the interface, resulting in an improvement in the fill factor. These effects result in a significant increase in the efficiency of non-fullerene solar cells based on PM6 and Y6, from 15.86 to 17.34%. In addition, we have found that the problem of the interface in contact with ITO occurs not only in PEDOT:PSS, but also in oxide-based charge transport layers. We have confirmed that the insertion of the WPFSCz- layer between ITO and an MoO3 (or ZnO) charge transport layer shows the same positive results.

While hole extraction is crucial for the external quantum efficiency of conventional n-i-p colloidal quantum dot (CQD) solar cells (CQDSCs), sulfur-passivated p-type CQDs (pCQDs) have been the best...

The fullerene acceptor, which has historically been used in bulk-heterojunction (BHJ) organic solar cells, is being replaced by non-fullerene acceptors due to its problem of high energy loss (Eloss). To reduce the energy loss in BHJ organic solar cells as a means to improve open-circuit voltage (Voc), several approaches have been applied to diminish recombination loss, notably enhancements to film morphology and decreasing of trap states by improving the crystallinity of active components. However, the adjustment of trap density by means of morphology control only has an inevitable limit. In this work, we have investigated the use of a ternary configuration as an alternative way to mitigate the energy loss in fullerene-based BHJ solar cells. A ternary system based on the wide-band-gap polymer PBDTTPD-HT, the small molecule DRCN5T, and PC71BM showed cascading charge transfer from PBDTTPD-HT through DRCN5T to PC71BM, an indirect electron transfer that avoided the deep charge transfer state between PBDTTPD-HT and PC71BM. DRCN5T:PC71BM mixture has a high ECT level close to the singlet state energy of DRCN5T, leading to low energy loss between DRCN5T and PC71BM and thereby greatly reducing the probability of first-order recombination. Consequently, the incorporation of a small amount of DRCN5T as a secondary donor into the PBDTTPD-HT:PC71BM system enhanced overall PCE, an effect mostly attributed to enhancement of Voc by means of eliminating charge transfer energy losses.

Although the power conversion efficiency (PCE) of inorganic perovskite-based solar cells (PSCs) has been considerably less than that of organic-inorganic hybrid PSCs due to their wider bandgap, inorganic perovskites are great candidates for the front cell in tandem devices. Herein, we demonstrate the great potential of low-temperature solution-processed two-terminal hybrid tandem solar cell devices based on spectrally matched inorganic perovskite and organic bulk heterojunction for the front and back cells, respectively. By matching optical properties of front and back cells in the hybrid tandem device by using CsPbI2Br and PTB7-Th:IEICO-4F BHJ as the active materials, we achieved a remarkably enhanced PCE in the hybrid tandem (18.04%) as compared to that of the single-junction device (12.46% for CsPbI2Br and 11.02% for PTB7- Th:IEICO-4F). Notably, the PCE of our hybrid tandem device is thus far the highest PCE among the reported tandem devices based on perovskite and organic material. Moreover, the long-term stability of inorganic perovskite devices under stress of humidity was improved in the hybrid tandem device due to the hydrophobicity of the PTB7-Th:IEICO-4F back cell. In addition, the potential promise of this type of hybrid tandem device was calculated, where a PCE of as much as 2 ~28% is possible by improving the external quantum efficiency and reducing energy loss in the sub-cells.

Porphyrin derivatives have recently emerged as hole transport layers (HTLs) because of their electron-rich characteristics. Although several successes with porphyrin-based HTLs have been recently reported, achieving excellent solar cell performance, the chances to improve this further by molecular engineering are still open. In this work, Zn porphyrin (PZn)-based HTLs were developed by conjugating fluorinated triphenylamine (FTPA) wings at the perimeter of the PZn core for low-temperature perovskite solar cells (L-PSCs). The fluorinated PZn-HTLs (PZn–2FTPA and PZn–3FTPA) exhibited superior HTL properties compared to the nonfluorinated one (PZn–TPA). Moreover, their deeper highest occupied molecular orbital energy levels were beneficial for boosting open-circuit voltages, and their enhanced face-on stacking improved the hole transport properties. The L-PSC using PZn–2FTPA achieved the highest performance of 18.85%. Thus far, this result is one of the highest reported power conversion efficiencies among the...

Perylene diimide (PDI) based high bandgap acceptors, DTBTP, DTF2BTP, and DTF2TZP, are synthesized for use in fullerene-free organic solar cells. The two PDI rings are connected to the end of the n-type core, forming a PDI-n-type core-PDI structure. Several n-type core materials, 4,7-dithieno-2,1,3-benzothiadiazole (DTBT), 5,6-difluoro-4,7-dithieno-2,1,3-benzothiadiazole (DTF2BT), and 4,6-difluoro-2H-benzo[d][1,2,3]triazole (DTF2TZ), are incorporated in the PDI acceptors and the n-type core effect on photovoltaic properties is studies. The introduction of alkyl side chains onto the core structure weakened the intermolecular interaction, whereas fluorination of the core structure improved the backbone planarity and intermolecular ordering. DTF2BTP having a planar core structure without bulky alkyl chains yielded the best power conversion efficiency, 4.41%, when mixed with PTB7-Th donor. The n-type core structure was beneficial in terms of increasing the electron accepting properties and the absorption in the high bandgap region of non-fullerene acceptors.

Summary Although the power conversion efficiency (PCE) of organic photovoltaic (OPV) devices has recently improved to more than 16%, halogenated solution processes are typically employed to obtain optimal performance. However, halogenated processing is harmful to health and the environment, which can be a significant obstacle to commercialization. Therefore, development of active materials processable under halogen-free conditions is of great importance in this field. In this study, a 16.04% OPV device, processed under halogen-free conditions, is developed by employing a new active-blend system, PBDTTPD-HT:BTP-2F-BO. It is highly soluble in halogen-free solvents, forming a preferential bulk-heterojunction morphology. The PBDTTPD-HT:BTP-2F-BO device achieves a PCE comparable with current state-of-the-art devices based on PBDB-TF:BTP-4F (also known as PM6:Y6) using a conventional halogenated process (16.40% versus 16.33%). Furthermore, it demonstrates a significantly higher PCE than the PBDB-TF:BTP-4F device with a halogen-free process (16.04% versus 9.70%).

Although the combination of wide band gap polymer donors and narrow band gap small-molecule acceptors achieved state-of-the-art performance as bulk heterojunction (BHJ) active layers for organic solar cells, there have been only several of the wide band gap polymers that actually realized high-efficiency devices over >10%. Herein, we developed high-efficiency, low-energy-loss fullerene-free organic solar cells using a weakly crystalline wide band gap polymer donor, PBDTTPD-HT, and a nonfullerene small-molecule acceptor, ITIC. The excessive intermolecular stacking of ITIC is efficiently suppressed by the miscibility with PBDTTPD-HT, which led to a well-balanced nanomorphology in the PBDTTPD-HT/ITIC BHJ active films. The favorable optical, electronic, and energetic properties of PBDTTPD-HT with respect to ITIC achieved panchromatic photon-to-current conversion with a remarkably low energy loss (0.59 eV).

A charge transport layer based on transition metal‐oxides prepared by an anhydrous sol–gel method normally requires high‐temperature annealing to achieve the desired quality. Although annealing is not a difficult process in the laboratory, it is definitely not a simple process in mass production, such as roll‐to‐roll, because of the inevitable long cooling step that follows. Therefore, the development of an annealing‐free solution‐processable metal‐oxide is essential for the large‐scale commercialization. In this work, a room‐temperature processable annealing‐free “aqueous” MoOx solution is developed and applied in non‐fullerene PBDB‐T‐2F:Y6 solar cells. By adjusting the concentration of water in the sol–gel route, an annealing‐free MoOx with excellent electrical properties is successfully developed. The PBDB‐T‐2F:Y6 solar cell with the general MoOx prepared by the anhydrous sol–gel method shows a low efficiency of 7.7% without annealing. If this anhydrous MoOx is annealed at 200 °C, the efficiency is recovered to 17.1%, which is a normal value typically observed in conventional structure PBDB‐T‐2F:Y6 solar cells. However, without any annealing process, the solar cell with aqueous MoOx exhibits comparable performance of 17.0%. In addition, the solar cell with annealing‐free aqueous MoOx exhibits better performance and stability without high‐temperature annealing compared to the solar cells with PEDOT:PSS., Annealing‐free solution‐processable aqueous MoOx are developed and applied in bulk‐heterojunction polymer solar cells based on non‐fullerene system PBDB‐T‐2F:Y6. The solar cells with aqueous MoOx exhibit higher efficiencies and better stabilities without high‐temperature annealing compared to the solar cells with PEDOT:PSS.

A carbon nanotube–titania (CNT-TiO2) composite that coats diapers has been synthesized and tested for the removal of ammonia (self-cleaning test) and Candida albicans fungi (selfsterilizing test), which cause unpleasant odors and candidiasis disease, respectively. The composite was characterized by FTIR, FESEM-EDX, XRD, and UV-Vis DRS. Results of XRD and UV-Vis DRS measurement showed that the CNT-TiO2 composite has a high crystalline and low band gap. The results of the self-cleaning and self-sterilizing tests showed that the optimum composition of the composite was 1–3 wt% of CNT and 97–99 wt% of TiO2. Acid treatment at pH 1 was accompanied by ultrasonic agitation in appropriate conditions for composite synthesis. Within 2 hours of testing, the modified diapers, at the optimum composite composition, can remove ammonia and C. albicans by 91% and 98%, respectively. The experimental results showed that ammonia and fungi on the modified diapers were removed up to the standard minimum values required to prevent odor and diaper rash.