Low-temperature-processed (100 °C) carbon paste was developed as counter electrode material in hole-conductor free perovskite/TiO2 heterojunction solar cells to substitute noble metallic materials. Under optimized conditions, an impressive PCE value of 8.31% has been achieved with this carbon counter electrode fabricated by doctor-blading technique. Electrochemical impedance spectroscopy demonstrates good charge transport characteristics of low-temperature-processed carbon counter electrode. Moreover, this carbon counter electrode-based perovskite solar cell exhibits good stability over 800 h.

No abstract

Perovskite solar cells (PSCs) has skyrocketed in the past decade to an unprecedented level due to their outstanding photoelectric properties and facile processability. However, the utilization of expensive hole transport materials (HTMs) and the inevitable instability instigated by the deliquescent dopants represent major concerns hindering further commercialization. Here, a series of low-cost, conjugated polymers are designed and applied as dopantfree HTMs in PSCs, featuring tuned energy levels, good temperature and humidity resistivity, and excellent photoelectric properties. Further studies highlight the critical and multifaceted roles of the polymers with respect to facilitating charge separation, passivating the surface trap sites of perovskite materials, and guaranteeing long-term stability of the devices. A stabilized power conversion efficiency (PCE) of 20.3% and remarkably enhanced device longevity are achieved using the dopant-free polymer P3 with a low concentration of 5 mg/mL, qualifying the device as one of the best PSC systems constructed on the basis of dopant-free HTMs so far. In addition, the flexible PSCs based on P3 also exhibit a PCE of 16.2%. This work demonstrates a promising route toward commercially viable, stable, and efficient PSCs.

conditions, such as the solvent and dopants used, as well as the doping concentrations. [ 5 ] Therefore, it is imperative to develop low-cost, dopant-free HTMs for effi cient PSCs. Most recently, impressive photovoltaic performance has been reported for different HTMs, such as small molecule-based HTMs, [29][30][31][32][33][34][35][36] polymer-based HTMs, [37][38][39][40] and inorganic hole conductors. [ 41,42 ] However, the vast majority of these reported HTMs require doping and the highest effi ciency reported in PSCs so far is less than 13%. Some novel HTMs, besides good hole mobilities, simultaneously show strong light absorbtion in the visible and near-infrared region. [ 34,35 ] Thus, these materials also have the potential to act as photoactive donor materials (PDMs) in bulk heterojunction (BHJ) organic solar cells (OSCs). [ 43,44 ] Herein, we report the design and synthesis of an acceptordonor-acceptor (A-D-A) structured small-molecule material M1 based on a rigid benzo[1,2b:4,5b′]-dithiophene (BDT) central building block and phenoxazine (POZ) linkers. With its unique properties, such as suitable energy levels, strong optical absorption in the visible region, and high hole mobility, M1 has been used both as HTM in (CH 3 NH 3 )PbI 3 -perovskite-based solar cells and as PDM in BHJ OSCs. Excellent PCE of 13.2% under 100 mW cm −2 irradiation was achieved using M1 as dopant-free HTM in PSCs, as compared to 12.4% obtained for devices containing the p-type doped Spiro-OMeTAD as HTM and 7.14% for the devices not containing any HTM. When applied in BHJ OSCs, a PCE of 6.91% was achieved using an optimized device structure of ITO/ZnO/polyethylenimine, 80% ethoxylated (PEIE)/ M1 :PC 70 BM (1:1.2)/MoO 3 /Ag. To the best of our knowledge, this is the fi rst case where a small-molecule organic material has been shown to act both as an HTM in PSCs and as a PDM in BHJ OSCs and showing excellent conversion effi ciencies in both types of solar cell systems.The structure and route of synthesis of the small-molecule material M1 are shown in Figure 1 and Scheme 1 , respectively. The BDT unit is rigid and fl at and is widely used as central building block in the construction of small-molecule donor materials for the application in BHJ OSCs, and this class of materials tend to exhibit high hole mobility and overall conductivity. [45][46][47][48][49] POZ is a well conjugated heterocyclic ring system with a butterfl y conformation and it is widely used in dyesensitized solar cells, possessing unique electronic and optical properties. [50][51][52][53] The BDT core unit was functionalized with ( Z )-3-(3-ethylrhodanine-5-alkenyl)-10-(2-ethylhexyl)-phenoxazine groups in order to generate a low band gap material. The symmetrical structure is expected to enhance π−π stacking interactions, which could be benefi cial for promoting a high hole The development of cost-effective, high-effi ciency solar cells that can meet the ever increasing demand of sustainable energy is one of the great challenges in the 21st century. Over the past two ye...

Low-cost transition metal-based electrocatalysts for water oxidation and understanding their structure−activity relationship are greatly desired for clean and sustainable chemical fuel production. Herein, a core− shell (CS) NiFeCr metal/metal hydroxide catalyst was fabricated on a 3D Cu nanoarray by a simple electrodeposition−activation method. A synergistic promotion effect between electronic structure modulation and nanostructure regulation was presented on a CS-NiFeCr oxygen evolution reaction (OER) catalyst: the 3D nanoarchitecture facilitates the mass transport process, the in situ formed interface metal/metal hydroxide heterojunction accelerates the electron transfer, and the electronic structure modulation by Cr incorporation improves the reaction kinetics. Benefiting from the synergy between structural and electronic modulation, the catalyst shows excellent activity toward water oxidation under alkaline conditions: overpotential of 200 mV at 10 mA/cm 2 current density and Tafel slope of 28 mV/dec. This work opens up a new window for understanding the structure−activity relationship of OER catalysts and encourages new strategies for development of more advanced OER catalysts.

Conjugated polymers are regarded as promising candidates for dopant-free hole-transport materials (HTMs) in efficient and stable perovskite solar cells (PSCs). Thus far, the vast majority of polymeric HTMs feature structurally complicated benzo­[1,2-b:4,5-b’]­dithiophene (BDT) analogs and electron-withdrawing heterocycles, forming a strong donor–acceptor (D–A) structure. Herein, a new class of phenanthrocarbazole (PC)-based polymeric HTMs (PC1, PC2, and PC3) has been synthesized by inserting a PC unit into a polymeric thiophene or selenophene chain with the aim of enhancing the π–π stacking of adjacent polymer chains and also to efficiently interact with the perovskite surface through the broad and planar conjugated backbone of the PC. Suitable energy levels, excellent thermostability, and humidity resistivity together with remarkable photoelectric properties are obtained via meticulously tuning the conformation and elemental composition of the polymers. As a result, PSCs containing PC3 as dopant-free HTM show a stabilized power conversion efficiency (PCE) of 20.8% and significantly enhanced longevity, rendering one of the best types of PSCs based on dopant-free HTMs. Subsequent experimental and theoretical studies reveal that the planar conformation of the polymers contributes to an ordered and face-on stacking of the polymer chains. Furthermore, introduction of the “Lewis soft” selenium atom can passivate surface trap sites of perovskite films by Pb–Se interaction and facilitate the interfacial charge separation significantly. This work reveals the guiding principles for rational design of dopant-free polymeric HTMs and also inspires rational exploration of small molecular HTMs.

No abstract

Two novel Acceptor-Donor-Acceptor (A-D-A) structured small molecular (SM-) materials POZ2 and POZ3 using an electron-rich phenoxazine (POZ) unit as a core building block were designed and synthesized. Their unique characteristics, such as suitable energy levels, strong optical absorption in the visible region, high hole mobility, and high conductivity, prompted us to use them both as p-type donor materials (DMs) in SM-bulk heterojunction organic solar cells (BHJ OSCs) and as hole transport materials (HTMs) in CH 3 NH 3 PbI 3 -based perovskite solar cells (PSCs). The POZ2based devices yielded promising power conversion efficiencies (PCEs) of 7.44% and 12.8% in BHJ OSCs and PSCs, respectively, which were higher than the PCEs of 6.73% (BHJ-OSCs) and 11.5% (PSCs) obtained with the POZ3-based devices. Moreover, our results demonstrated that the POZ2 employing the electron-deficient benzothiazole (BTZ) as linker exhibited higher hole mobility and conductivity than that of the POZ3 using thiophene as linker, leading to better device performance both in BHJ-OSCs and PSCs. These results also provide guidance for the molecular design of high charge carrier mobility SM-materials for highly efficient BHJ OSCs and PSCs in the future.