Here, we report that the performance of perovskite solar cells (PSCs) can be improved by aggregation control in polyelectrolytes interlayer. Through counterions tailoring and solvent optimization, the strong aggregation of polyelectrolytes P3CT-Na can be broken up by P3CT-CH3NH2. When using P3CT-CH3NH2 to replace P3CT-Na as hole transport layer, the average efficiency is greatly improved from 16.9 to 18.9% (highest 19.6%). Importantly, efficiency over 15% is obtained in 1 cm2 devices with P3CT-CH3NH2, ∼50% higher than that with P3CT-Na (10.3%). Our work demonstrates the important role of aggregation control in polyelectrolytes interlayer, providing new opportunities to promote its application in PSCs.Keywords: aggregation control; counterions; hole transport layer; perovskite solar cells; polyelectrolytes;

Landmark power conversion efficiency (PCE) over 10% has been accomplished in the past year for single-junction organic solar cell (OSCs), suggesting a promising potential application of this technology. However, most of the high efficient OSCs are based on inverted configuration. Regular structure OSCs with both high efficiency and good stability are still rarely reported to date. In this work, by utilizing a new designed ligand-free and non-thermal-annealing-treated Al-doped ZnO cathode interlayer, high efficiency and greatly improved stability are simultaneously realized in regular OSCs. The highest PCE of 10.14% is accomplished for single-junction regular OSCs with active blend of poly [[2,6′-4,8-di(5-ethylhexylthienyl)benzo[1,2-b;3,3-b]dithiophene][3-fluoro-2[(2-ethylhexyl)carbonyl]thieno [3,4-b]thiophenediyl]] (PTB7-Th):[6,6]-phenyl C71-butyric acid methyl ester (PC71BM). Excellent device stability is confirmed as well, by keeping 90% of its initial PCE value after 135 d in N2, and 80% of its initial PCE value after 15 d in ambient air, respectively. Furthermore, the applicability of the designed interlayer in regular OSCs is demonstrated by other active blend systems, including the nonfullerene material. This work highlights that high efficiency and good stability can be realized simultaneously in regular OSCs as well, and will provide referential strategy and methodology for this target.

AbstractFullerene derivatives, which possess extraordinary geometric shapes and high electron affinity, have attracted significant attention for thin film technologies. This study demonstrates an important photovoltaic application using carboxyl-functionalized carbon buckyballs, C60 pyrrolidine tris-acid (CPTA), to fabricate electron transport layers (ETLs) that replace traditional metal oxide-based ETLs in efficient and stable n-i-p-structured planar perovskite solar cells (PSCs). The uniform CPTA film is covalently anchored onto the surface of indium tin oxide (ITO), significantly suppressing hysteresis and enhancing the flexural strength in the CPTA-modified PSCs. Moreover, solution-processable CPTA-based ETLs also enable the fabrication of lightweight flexible PSCs. The maximum-performing device structures composed of ITO/CPTA/CH3NH3PbI3/2,2′,7,7′-tetrakis-(N,N-di-p-methoxyphenylamine)-9,9′-spirobifluorene (spiro-OMeTAD)/Au yield power conversion efficiencies of more than 18% on glass substrates and up to 17% on flexible substrates. These results indicate that the CPTA layers provide new opportunities for solution-processed organic ETLs by substantially simplifying the procedure for fabricating PSCs for portable applications.

•A new carboxylate functionalized small molecule non-conjugated zwitterion, HDAC was synthetized.•HDAC could effectively lower the work function of Ag cathode.•PSCs using solution processed HDAC layer achieved a PCE of 17.10% with a high fill factor of 80%.•The flexible HDAC device based on PET substrate showed a PCE over 14%.A new carboxylate functionalized small molecule non-conjugated zwitterion, HDAC was proposed for its feasible one-step synthetic procedure. It can be used as an efficient interlayer to improve the fullerene/cathode interface of inverted planar heterojunction perovskite solar cells. A HDAC modified device could increase the power conversion efficiency from 15% to 17%. The main increase of the performance parameter lies on the increase of fill factor from around 72% to 80%, which could be attributed to the formation of interface dipole and elimination of potential barrier at the interface of electron transporting layer and cathode. This work brings up a simple design principle for efficient interfacial materials in perovskite solar cells.Download high-res image (253KB)Download full-size image

A novel small-molecule, B2F, which is based on benzobis(thiadiazole), was designed and synthesized as an electron extraction material for perovskite solar cells (PSCs). Because of the high electron affinity of the benzobis(thiadiazole) unit and the Pb–S bonding, B2F exhibited good adhesion on the perovskite surface and an efficient photoluminescence quenching to CH3NH3PbI3. The simple device with B2F as the solution-processing electron extraction layer without any extra interface layer exhibited an optimal power-conversion efficiency (PCE) of 12.35%. The B2F-based device can be further improved by the addition of C60/BCP as efficient electron transport and hole-blocking layers to enhance electron transport and prevent carrier leakage. A champion PCE of 17.18% was achieved with an open-circuit voltage of 1.052 V, a short-circuit current density of 20.63 mA cm−2 and a fill factor of 79.15%. In summary, we developed an efficient electron extraction material for PSCs, which represents a new building block for the design and development of highly efficient electron transport materials for PSCs in the future.

A PTB7-based cationic narrow band-gap polyelectrolyte, named PTB7-NBr, has been designed and synthesized as a cathode interfacial material for polymer solar cells. PTB7-NBr exhibits excellent cathode interfacial modification in solar cells with PTB7 and PTB7-Th as donor polymer and a high PCE of 9.24% was achieved.

The performance of organic solar cells (OSCs) with edetate electrolytes depends on external bias, and ions are speculated to be responsible for this phenomenon. To clarify the detailed relationship between the ions of electrolytes and the bias-dependent behaviors of devices, this work introduces four edetate cathode interlayers (EDTA-X, X = nH(4–n)Na, n = 0, 1, 2, and 4) containing different kinds and number of cations into inverted OSCs. The results show that the devices initial and saturated (after external bias treatment) power conversion efficiencies (PCEs) both decrease with the increase in the number of H+. Moreover, the bias-dependent degrees increase with the increase in H+ number; with that, the PCE increment of EDTA-4H device is 53.4%, while that of the EDTA-4Na device is almost unchanged. The electrical impedance spectroscopy and capacitance–voltage tests reveal that the interfacial recombination is greatly suppressed by external bias treatment, which is not a result of the decreased density of defect states. The results indicate that the ion’s motion, specifically the H+ motion, under external electrical field is responsible for the bias-dependent behavior, which is conducive to the design of new efficient electrolytic interlayers without bias-dependent performance.Keywords: cathode interlayer; edetate electrolytes; external bias; ion motion; organic solar cells;

Phenanthroline based organic semiconductors (BCP, Bphen, Mphen, and Phen) are used to hybrid with CdS as cathode interlayers in inverted organic solar cells (OSCs). We observed that selecting the polar solvent and hydrophobic interlayers with a diphenyl group could improve the performance of the organic photovoltaic devices. The modification to CdS can effectively improve its electron mobility, film morphology, interfacial contact, and energy level alignment, which finally leads to a significant enhancement of device performance. Through incorporating the CdS–P hybrids (CdS–BCP, CdS–Bphen, CdS–Mphen, and CdS–Phen) as cathode buffer layers, the device PCE (PTB7:PC71BM as the active layer) is greatly improved from 3.09% to 8.36, 7.84, 6.69, and 6.57%, respectively, compared with devices fabricated on the pristine CdS interlayer. These results indicate that the common inorganic semiconductor like CdS can be modified using some organic semiconductors to produce general applicable electron transport layers applied in OSCs. Our work puts forward new insights for the development of new interface modification materials and fabrication of high efficiency devices.

Environmentally benign hybrid interlayers are prepared by modifying the zinc sulfide (ZnS) with phenanthroline/derivatives and utilized in inverted polymer solar cells (PSCs). Performances of the inverted PSCs are improved enormously by incorporating these hybrid interlayers, as which can effectively improve the energy level alignment, electron mobility, surface morphology, and interfacial contact. Greatly improved power conversion efficiencies (PCEs) of 7.79%, 8.00%, 7.47%, and 7.56% are achieved with these hybrid interlayers ZnS-BCP, ZnS-Bphen, ZnS-Mphen, and ZnS-Phen, respectively, compared to the PCE of 2.99% of the reference ZnS-based device, based on PTB7:PC71BM active layer. Our results demonstrate that hybrid interfacial materials comprising inorganic and organic semiconductor possess promising potential to improve the performance of organic electronic devices, and set an example to develop this novel class of interfacial materials for electronic devices.Keywords: cathode; hybrid interlayer; inverted polymer solar cells; phenanthroline; ZnS

Organic ionic materials have been reported to be efficient cathode interlayer (CIL) materials in polymer solar cells (PSCs); however, most of them are employed in conventional PSCs. For an inverted structural device which has better stability, the efficiency is still far from expectation and the report is also limited. In this study, by using nonconjugated zwitterions as the CIL and inverted structure, the power conversion efficiency (PCE) is ∼6%, though the PCE can reach 9.14% in the conventional device. By introducing polyethylene glycol (PEG) into the zwitterions, the PCE of the inverted PSCs was improved ∼33% and reached ∼8% mainly because of the enhancement of the open-circuit voltage (Voc) and fill factor (FF). Further research on the device parameters, work functions, morphology of indium tin oxide (ITO) with various CILs, and recombination resistance of the devices indicated that PEG + zwitterion induced not only a lower work function of ITO but also a more uniform morphology of CILs with less contact of the photoactive layer with ITO, which induced suppressed charge recombination and a higher Voc and FF. Enhanced ability in interface modification of PEG + zwitterion CILs displayed a simple and feasible approach to elevate the performance of inverted PSCs with ionic CILs.

•F8BT modify the perovskite interface of perovskite solar cells.•F8BT delivered hugely enhanced PCE 13.9% compared to the PCE 7.9% of the reference.•Greatly eliminated hysteresis was recorded F8BT devices.•Promising interfacial materials and possible approach to eliminate the hysteresis of PSCs.A conjugated polymer poly (9,9-dioctyfluorene-co-benzothiazole) (F8BT) was used as the electron transporting layer (ETL) to modify the cathode interface of inverted planar perovskite solar cell. Incorporation of the thin F8BT layer delivered greatly enhanced power conversion efficiency (PCE) of 13.9% compared to the PCE 7.9% of the device without F8BT, due to the improvements in various performance parameters like Voc, Jsc and FF. Moreover, great elimination of the hysteresis was demonstrated in F8BT based devices. These results suggest promising potential of polymeric materials in perovskite solar cells and possible approach to eliminate the hysteresis of perovskite solar cells with this class of interfacial materials.

The cathode interlayer is essential to bulk heterojunction polymer solar cells (PSCs). As we all know, most of the organic interfacial materials are amino derivatives, including neutral amine derivatives and ammonium derivatives. Herein, a non-amino small molecule, TBT-a, with sulfonate anionic pendants was synthesized and interface modification was investigated. The PSC with TBT-a as the cathode interlayer exhibited a high power conversion efficiency of 8.68%. We found that the TBT-a interlayer simultaneously enhanced all the device parameters, probably by inducing an effective interface dipole, altering the optical distribution, and enhancing the electron mobility. These results indicated that sulfonate interfacial materials could play a similar role as amine-based interfacial materials in interface modification.

In this study, ferrocenedicarboxylic acid (FDA) has been introduced between an ITO electrode and ZnO interlayer to improve the performance of inverted polymer solar cells. The highest power conversion efficiency (PCE) of 9.06% is achieved among the measurements. Besides, the average PCE of FDA/ZnO based devices is observed with 11.9% enhancement (8.73% vs. 7.80%) compared to ZnO-only devices. Electrical characterization, surface morphology, wetting properties, as well as exciton generation rate and dissociation probability were investigated to understand the impact of FDA insertion on the interfacial properties. It was found that exciton dissociation efficiency and charge collection efficiency were significantly improved after inserting FDA, while the surface morphology, average roughness and water contact angle of the ZnO film were not changed. It was thought that FDA connected to the ITO electrode and ZnO film because of its carboxyl groups, which lead to a compact interfacial contact and reduced charge recombination. In addition, the devices based on the FDA/ZnO interlayers displayed improved stability in the argon-filled glove box without any encapsulation for about 1000 h compared to the ZnO-only devices. This study provides a new idea to introduce materials with functional groups between ITO/metal oxides interfaces to achieve more efficient charge collection and device performance.

•A simple chlorobenzene vapor assistant annealing (CB VAA) method has been developed for the first time to produce high quality perovskite films.•It was found that this method had a positive effect on the interfacial contact between perovskite and PCBM.•Planar heterojunction perovskite solar cells produced by this method possessed enhanced Jsc, PCE with reduced hysteresis.•Various measurements were conducted to investigate the influence of CB VAA method on perovskite films, interface properties as well as perovskite solar cells.In this study, chlorobenzene (CB) vapor assistant annealing (VAA) method is employed to make high quality perovskite films and produce high efficiency CH3NH3PbI3-xClx perovskite solar cells. The perovskite films made by this method present several advantages such as increased crystallinity, large grain size and reduced crystal boundaries compared with those prepared by thermal annealing (TA) method, which is beneficial to charge dissociation and transport in hybrid photovoltaic device. In addition, it is found that the CB VAA method could improve the surface property of perovskite film, resulting in a preferable coverage of PCBM layer and a better interfacial contact between perovskite film and upper PCBM film. Consequently, the short circuit current density (Jsc) of the devices is significantly increased, yielding a high efficiency of 14.79% and an average efficiency of 13.40%, which is 13% higher than that of thermal annealed ones. This work not only put forward a simple and efficient approach to prepare highly efficient perovskite solar cells but also provide a new idea to improve the morphology and interfacial contact in one integration step.Chlorobenzene(CB) vapor assistant annealing process was utilized as a simple and effective method to produce perovskite films in high quality. It was also found that the spreadability of PCBM on perovskite layer could be improved through this procedure at the same time. So, enhanced Jsc, PCE as well as a reduced hysteresis were obtained in the photovoltaic devices.

Organic electrolyte interlayer has been widely used in organic solar cells (OSCs). However, previous reports mainly focused on conventional OSCs despite with poor stability. In more stable inverted OSCs, the application of organic electrolyte interlayer is rarely reported and the device efficiency is low. Here, a simple nonconjugated small molecule electrolyte (SME), ethylene diamine tetraacetic acid tetrasodium (EDTA-4Na), is successfully introduced into inverted OSCs as a cathode interlayer, leading to a high efficiency of 9.69%. Besides efficiency, the device stability is also improved and almost 85% of the efficiency can be maintained even after storage of 46 days. More importantly, EDTA-4Na tremendously alleviates the hysteresis phenomenon happening in organic optoelectronic devices based on ionized interlayer. As a result, stabilized power output of ∼9.5% is obtained in OSCs with EDTA-4Na. These inspiring results prove that electrolytes with simple structure can also achieve excellent performance and that nonconjugated SME is also a competitive candidate as cathode interlayer, especially in inverted OSCs.

Organic–inorganic perovskite solar cells have recently emerged at the forefront of photovoltaics research. Here, for the first time, graphdiyne (GD), a novel two dimension carbon material, is doped into PCBM layer of perovskite solar cell with an inverted structure (ITO/PEDOT:PSS/CH3NH3PbI3–xClx/PCBM:GD/C60/Al) to improve the electron transport. The optimized PCE of 14.8% was achieved. Also, an average power conversion efficiency (PCE) of PCBM:GD-based devices was observed with 28.7% enhancement (13.9% vs 10.8%) compared to that of pure PCBM-based ones. According to scanning electron microscopy, conductive atomic force microscopy, space charge limited current, and photoluminescence quenching measurements, the enhanced current density and fill factor of PCBM:GD-based devices were ascribed to the better coverage on the perovskite layer, improved electrical conductivity, strong electron mobility, and efficient charge extraction. Small hysteresis and stable power output under working condition (14.4%) have also been demonstrated for PCBM:GD based devices. The enhanced device performances indicated the improvement of film conductivity and interfacial coverage based on GD doping which brought the high PCE of the devices and the data repeatability. In this work, GD demonstrates its great potential for applications in photovoltaic field owing to its networks with delocalized π-systems and unique conductivity advantage.

A small-molecule electrolyte based on the popular ethylene diamine tetraacetic acid (EDTA-N) is introduced as an efficient cathode interlayer in inverted polymer solar cells, helping to deliver power conversion efficiency over 9%. The strong dependence of device performance on the external bias suggests that the ion motion plays a critical role in improving the performance of devices with electrolyte interlayers.

Using polyelectrolytes (P3CT-Na) as hole-transporting materials (HTMs), high performance inverted perovskite solar cells with a PCE of 16.6% could be obtained, which was more than 20% improvement compared with those based on the PEDOT:PSS HTM (PCE of 13.7%). The performance improvement can be ascribed to the desirable match of energy levels as well as the better crystalline properties and larger grain size of CH3NH3PbCl3−xIx films on P3CT-Na. Importantly, rather good performance with PCE over 11% is achievable even if the P3CT-Na thickness ranges from 1 nm to 52 nm. Our work indicated the promising applications of polyelectrolyte based HTMs in perovskite solar cells and may provide some insights into the design and synthesis of new HTMs to further improve the device performance.

In this study, a high-performance inverted polymer solar cell (PSC) has been fabricated by incorporating a zinc oxide (ZnO)/light-harvesting complex II (LHCII) stacked structure as the cathode interlayer. The LHCII not only smoothens the film surface of ZnO, improves the contact between ZnO and the photoactive layer, but also suppresses the charge carrier recombination at the interface, hence all the device parameters of PTB7-based solar cells are simultaneously improved, yielding higher power conversion efficiency (PCE) up to 9.01% compared with the control one (PCE 8.01%). And the thin LHCII modification layer also presents similar positive effects in the PTB7-Th:PC71BM system (PCE from 8.31% to 9.60%). These results put forward a facile approach to the interfacial modification in high-performance PSCs and provide new insight into developing and utilizing inexpensive and environmentally friendly materials from the fields of biological photosynthesis.Keywords: cathode; inverted polymer solar cells; LHCII; modification interlayer; ZnO nanoparticles

Three amino-functionalized fluorene oligomers with different solubility were developed as cathode interfacial materials for inverted polymer solar cells (I-PSCs). By side chain design, we solved the interface layer erosion problem for I-PSCs, and the devices exhibit a power conversion efficiency as high as 8.94%.

•Planar heterojunction CH3NH3PbI3−xClx perovskite solar cells were fabricated through a low-temperature solution process.•The performance of perovskite solar cells was enhanced after isopropanol treatment.•The improved performance was attributed to the remove of excess CH3NH3I in perovskite film and modified interfacial properties.Hybrid organic/inorganic perovskite planar heterojunction (PHJ) solar cells are becoming one of the most competitive emerging technologies. Here, the devices (ITO/PEDOT:PSS/CH3NH3PbI3−xClx/PC60BM/C60/Al) are fabricated based on solution process. A power conversion efficiency (PCE) up to 13.1% was obtained after isopropanol (IPA) solvent treatment, which was 9% improvement than that of the original devices. Photocurrent hysteresis could be reduced to a certain extent by introducing IPA treatment. Solvent treatment can remove as-grown impurities like CH3NH3I and defects formed during the device fabrication. We also demonstrated the electrical and optical properties of perovskite films were improved. The addition of IPA-treated facilitates the formation of a relatively smooth PC60BM films. This work provides a very simple but effective strategy to enhance the power conversion efficiency of perovskite solar cells.

•Planar heterojunction perovskite solar cells were successfully fabricated through a low-temperature solution process.•The performance of perovskite solar cells was found to strongly depend on the external bias treatment.•Ions motion under the external bias was considered to be the potential reason for the dependence of external bias.Planar heterojunction perovskite solar cells were fabricated through a low temperature approach. We find that the device performance significantly depends on the external bias before and during measurements. By appropriate optimization of the bias conditions, we could achieve an 8-fold increase in the power conversion efficiency. The significant improvement in device performance might be caused by the ion motion in the perovskite under the external electric field.

We reported the favorable cathode buffer layer based on a blend of ZnO nanoparticles (NPs) and TiO2 nanorods (NRs) applied to inverted solar cells. In addition to the high optical transmittance, the resultant blend film gave a relatively dense film with lower roughness than that of the respective single-component film. This improved the interface contact between the buffer layer and photoactive layer and therefore reduced the contact resistance and leakage current. Moreover, the combination of NRs and NPs increased the efficiency of electron transport and collection by providing both a direct path for electron transport from TiO2 NRs and a large contact area between ZnO NPs and the active layer. Consequently, both the short-circuit current density (Jsc) and fill factor (FF) in the device were improved, leading to an improvement of the device performance. The best power conversion efficiency (PCE) based on the blend film as the buffer layer reached 8.82%, which was preferable to those of a single ZnO NP film (7.76%) and a TiO2 NR-based device (7.66%).Keywords: blend film; cathode buffer layer; inverted solar cells; TiO2 nanorods; ZnO nanoparticles;

Disodium edetate (EDTA-Na), a popular hexadentate ligand in analytical chemistry, was successfully introduced in organic solar cells (OSCs) as cathode interfacial layer. The inverted OSCs with EDTA-Na showed superior performance both in power conversion efficiency and devices stability compared with conventional devices. Interestingly, we found that the performance of devices with EDTA-Na could be optimized through external bias treatment. After optimization, the efficiency of inverted OSCs with device structure of ITO/EDTA-Na/polymer thieno[3,4-b]thiophene/benzodithiophene (PTB7):PC71BM/MoO3/Al was significantly increased to 8.33% from an initial value of 6.75%. This work introduces a new class of interlayer materials, small molecule electrolytes, for organic solar cells.Keywords: external bias; interlayer; organic solar cells; small molecule electrolytes

ZnO nanofilm as a cathode buffer layer has surface defects due to the aggregations of ZnO nanoparticles, leading to poor device performance of organic solar cells. In this paper, we report the ZnO nanoparticles aggregations in solution can be controlled by adjusting the solvents ratios (chloroform vs methanol). These aggregations could influence the morphology of ZnO film. Therefore, compact and homogeneous ZnO film can be obtained to help achieve a preferable power conversion efficiency of 8.54% in inverted organic solar cells. This improvement is attributed to the decreased leakage current and the increased electron-collecting efficiency as well as the improved interface contact with the active layer. In addition, we find the enhanced maximum exciton generation rate and exciton dissociation probability lead to the improvement of device performance due to the preferable ZnO dispersion. Compared to other methods of ZnO nanofilm fabrication, it is the more convenient, moderate, and effective to get a preferable ZnO buffer layer for high-efficiency organic solar cells.Keywords: aggregations of ZnO nanoparticles; cathode buffer layer; inverted organic solar cells; mixed solvents

We reported a significant improvement in the efficiency of organic solar cells by introducing hybrid TiO2:1,10-phenanthroline as a cathode buffer layer. The devices based on polymer thieno[3,4-b]thiophene/benzodithiophene:[6,6]-phenyl C71-butyric acid methyl ester (PTB7:PC71BM) with hybrid buffer layer exhibited an average power conversion efficiency (PCE) as high as 8.02%, accounting for 20.8% enhancement compared with the TiO2 based devices. The cathode modification function of this hybrid material could also be extended to the poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methyl ester (P3HT:PC61BM) system. We anticipate that this study will stimulate further research on hybrid materials to achieve more efficient charge collection and device performance.Keywords: 1,10-phenanthroline; hybrid buffer layer; inverted OSC; TiO2;

Highly efficient organic solar cells were successfully demonstrated by incorporating a solution-processed cesium stearate between the photoactive layer and metal cathode as a novel cathode interfacial layer. The analysis of surface potential change indicated the existence of an interfacial dipole between the photoactive layer and metal electrode, which was responsible for the power conversion efficiency (PCE) enhancement of devices. The significant improvement in the device performance and the simple preparation method by solution processing suggested a promising and practical pathway to improve the efficiency of the organic solar cells.Keywords: cesium stearate; efficiency; interfacial layer; organic solar cells; solution-processed;

•ZnO nanoparticles (NPs) modified with C60 pyrrolidine tris-acid ethyl ester (PyC60) are introduced in inverted polymer solar cells as cathode buffer layer.•The morphology improvement of the PyC60/ZnO bilayer film contributes to reducing series loss and interfacial charge recombination.•The preferable interfacial contact between ZnO/PyC60 bilayer film and photoactive layer lowers electron injection barrier between photoactive layer and ZnO film.•The ZnO/PyC60 device based on a blend of PTB7:PC71BM as photoactive layer exhibits higher FF of 72.5% and PCE of 8.76%, respectively.In this paper, we reported that ZnO nanoparticles (NPs) film modified with C60 pyrrolidine tris-acid ethyl ester (PyC60) was used as cathode buffer layer in inverted polymer solar cells. The resultant device with a blend of PTB7:PC71BM as photoactive materials exhibited an open-circuit voltage (Voc) of 0.753 V, a short-circuit current (Jsc) of 16.04 mA cm−2, a fill factor (FF) of 72.5%, and an overall power conversion efficiency (PCE) of 8.76%. It was higher than the control devices based on sole ZnO NPs film or ZnO: PyC60 hybrid film as cathode buffer layer. It was found that the morphology improvement of ZnO/PyC60 film contributed to reducing series loss and interfacial charge recombination. In addition, it improved the interfacial contact with photoactive layer. The results increased electron injection and collection efficiency, and improved FF.ZnO nanoparticles (NPs) modified with C60 pyrrolidine tris-acid ethyl ester (PyC60) are introduced in inverted polymer solar cells as cathode buffer layer. The morphology improvement of the ZnO/PyC60 bilayer film contributes to reducing series loss and interfacial charge recombination. Consequently, the resultant inverted solar cells exhibit an overall power conversion efficiency (PCE) of 8.76%.

We used cesium stearate (CsSt) to modify the interface of the electron-extracting contact in inverted organic solar cells. Surface microstructure, optical properties, and electrical characterization as well as exciton generation rate and dissociation probability were investigated to understand the impact of CsSt on the interface contact. The results indicated that by incorporation of CsSt, the surface morphology and energy level as well as conductivity of a zinc oxide (ZnO) film were improved. On the basis of the above properties, highly efficient inverted organic solar cells have been demonstrated by using a ZnO nanoparticle film and CsSt stacked bilayer structure as the cathode interfacial layer. The insertion of a CsSt layer between the ZnO film and active layer improved the electron extraction efficiency, and a high power conversion efficiency (PCE) of 8.69% was achieved. The PCE was improved by 20% as compared to the reference device using a ZnO-only electron extraction layer.Keywords: Cesium stearate; Exciton dissociation; Interfacial modification; Organic solar cells

•We have developed a facile sol–gel method to synthesize CuS NCs.•The pyridine capped CuS NCs can be used directly as interfacial layer without ligand-exchange.•The hydrophilic CuS NCs can be exchanged with OAm and OA rapidly at room temperature and present hydrophobic characteristic.•The CuS NCs possess the superior interfacial property and can be processed in lower temperature than other metal oxide.CuS NCs were synthesized via a facile sol–gel method without post-thermal treatment. The as-prepared CuS NCs were analyzed and confirmed by XRD, HR-TEM, EDS and XPS as hexagonal covellite CuS. The average diameter of the samples was about 3 nm with narrow size distribution. CuS NCs can form a thin and smooth film without ligand-exchange that can be used as hole transport layer in organic solar cell. These hydrophilic CuS NCs with pyridine ligands can be exchanged with OAm and OA rapidly at room temperature and present hydrophobic characteristic, resulting in forming oil-soluble CuS NCs. This makes it possible tuning the surface property of CuS NCs and has the potential application for different fields.

We reported a significant improvement in the efficiency of polymer solar cells by introducing C60 pyrrolidine tris-acid (CPTA) to modify the interface between inorganic TiO2 nanorods and the organic active layer. The devices with CPTA-modified TiO2 as the cathode buffer layer exhibited a power conversion efficiency (PCE) as high as 8.74%, accounting for a 12.8% enhancement compared with the bare TiO2 based devices (7.75%) in the polymer thieno[3,4-b] thiophene/benzodithiophene:[6,6]-phenyl C71-butyric acid methyl ester (PTB7:PC71BM) system. We found that the CPTA layer improves the surface properties of the bare TiO2 film so that charge transfer between the active layer and the TiO2 layer is enhanced.

•We have developed an in situ method to prepare MoO3 thin film.•The composition and microstructure of the thin film were studied.•The MoO3 film possessed columnar morphology.•The MoO3 film was proved to have superior property in organic photovoltaics.Columnar MoO3 in situ growth prepared from direct converting soluble Mo-containing precursor during active layer thermal annealing was utilized as anode buffer layer to fabricate organic bulk heterojunction photovoltaics. The columnar morphology could improve the interface contact between active layer and buffer layer. The structure and phase of in situ formed MoO3 were studied by X-ray powder diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). We demonstrated that the organic photovoltaic devices based on P3HT:PC61BM using in situ formed columnar MoO3 as anode buffer layer presented a high open-circuit voltage and fill factor leading to an efficiency of 3.92%, which is higher than the controlled PEDOT:PSS-based devices.Graphical abstractColumnar MoO3 in situ growth prepared from direct converting soluble Mo-containing precursor during active layer annealing in organic photovoltaic device fabrication was utilized as anode buffer layer which simultaneously increase short circuit current and fill factor, resulting in enhanced device efficiency.

Two novel star-shaped donor–acceptor small molecules, TPA–TBT–CN and TPA–TBT–R, with triphenylamine (TPA) as the core, benzothiadiazole (BT) as the arm, and alkyl cyanoacetate or 3-ethylrhodanine as the end-group are synthesized for application as donor materials in OSCs. The two small molecule films show broad absorption bands from 300 nm to 850 nm, narrow optical band gaps (1.5–1.7 eV), deep HOMO energy levels (−5.0 to −5.1 eV) and moderate hole mobilities. OSCs based on blends of the two donors and PC70BM acceptors exhibit power conversion efficiencies of 1.34% and 1.79%, respectively. Notably, TPA–TBT–R with 3-ethylrhodanine as the end-group displays a broader solar spectral coverage, a lower HOMO level, a higher hole mobility and higher photovoltaic properties. Our results indicate that 3-ethylrhodanine as the acceptor and end-group is a promising linker in constructing donor materials for high efficiency OSCs.

Three new small organic molecules, I, II and III, consisting of dithienosilole as the central core, bithiophene bridge with different alkyl group substituents, and octyl cyanoacetate or dicyano unit as different end units, have been designed and synthesized. The thermal, optical, electrochemical and photovoltaic properties of these three compounds have been investigated. The solubility, absorption, energy levels and band gaps of these materials were effectively tuned by different alkyl groups substituted on the thiophene unit and/or different electron-withdrawing end groups. Bulk heterojunction solar cells with molecules I–III as electron donors and PC60BM ([6,6]-phenyl-C60-butyric acid methyl ester) as an election acceptor exhibited power conversion efficiencies of 3.27, 2.88 and 3.81% for I, II and III, respectively. All of these solar cells showed very high Voc values of 0.89–0.92 V, and the high Voc is consistent with the low-lying HOMO level of the donor. These compounds also have low LUMO levels which ensure effective charge transfer from the donor to the fullerene acceptor. The structure–photovoltaic property relationships of these donor materials were investigated and discussed.

A highly efficient polymer solar cell was fabricated using a polar fullerene derivative C60 pyrrolidine tris-acid (CPTA) as the cathode buffer layer. By introducing CPTA, the Voc, Jsc and FF were all much enhanced simultaneously. The power conversion efficiency (PCE) was significantly improved to 7.92%, which outperformed the device using Ca/Al as the cathode in our experiment.

We reported a facile solution-processed method to fabricate a MoSx anode buffer layer through thermal decomposition of (NH4)2MoS4. Organic solar cells (OSCs) based on in situ growth MoSx as the anode buffer layer showed impressive improvements, and the power conversion efficiency was higher than that of conventional PEDOT:PSS-based device. The MoSx films obtained at different temperatures and the corresponding device performance were systematically studied. The results indicated that both MoS3 and MoS2 were beneficial to the device performance. MoS3 could result in higher Voc, while MoS2 could lead to higher Jsc. Our results proved that, apart from MoO3, molybdenum sulfides and Mo4+ were also promising candidates for the anode buffer materials in OSCs.Keywords: buffer layer; bulk heterojunction; molybdenum disulfide; organic solar cells;

A novel hybrid material CdS/2,9-Dimethyl-4,7-diphenyl-1,10-phenanthroline (CdS·BCP) was prepared from the decomposition of its organic soluble precursor complex Cd(S2COEt)2·(BCP) by low-temperature treatment. CdS·BCP, which integrated the favorable properties of solvent durability, and high electron mobility of CdS as well as the good hole blocking property of BCP, was designed and developed as the interface modification material to improve electron collection in bulk heterojunction organic solar cells (OSCs). The inverted OSCs with CdS·BCP as buffer layer on ITO showed improved efficiency compared with the pure CdS or BCP. Devices with CdS·BCP as interlayer exhibited excellent stability, only 14.19% decay of power conversion efficiencies (PCEs) was observed (from 7.47% to 6.41%) after stored in glovebox for 3264 h (136 days). Our results demonstrate promising potentials of hybrid materials as the interface modification layers in OSCs, and provide new insights for the development of new interface modification materials in the future.Keywords: BCP; CdS; hybrid; interface; inverted; OSCs;

A new solid-contact Ag+-selective electrode was prepared with 9,10,12,13,24,25-hexahydro-5H,15H,23H-dibenzo[b,q][1,7,10,13,19,4,16]-entathiadiazacyclodocosine-6,16(7H,17H)-dione as ionophore, and α,ω-dihexylsexithiophene (DH-6T) ion-to-electron transducer. The sensor exhibited a working concentration range of 10−8 to 10−3 mol/L, with a near-Nernstian slope of 55.1 ± 0.2 mV/dec and detection limit of 1.7 × 10−9 mol/L. The fabricated electrodes demonstrated excellent selectivity over the most common monovalent and divalent cations.

A PTB7-based cationic narrow band-gap polyelectrolyte, named PTB7-NBr, has been designed and synthesized as a cathode interfacial material for polymer solar cells. PTB7-NBr exhibits excellent cathode interfacial modification in solar cells with PTB7 and PTB7-Th as donor polymer and a high PCE of 9.24% was achieved.

Two novel star-shaped compounds with 1,3,5-triazine as the core and fluorene as the arms, denoted as Tf1 and Tf2, were designed and synthesized. Compared with Tf1, Tf2 was found to have a π-extended structure with its additional inner fluorene arms. Owing to the diethylamino end groups, both compounds reduced the work function of ITO effectively. Enhanced device performances were obtained by incorporating these compounds as the cathode interlayers in inverted polymer solar cells with PTB7:PC71BM as the active layer. As revealed by Kelvin probe measurements, the work function of Tf1-modified ITO was lower than that of Tf2-modified ITO. As shown by atomic force microscopy (AFM), the morphology of the Tf1-coated surface was relatively smooth and homogenous, which provided a relatively good contact between the active layer and the cathode. As a result, a power conversion efficiency (PCE) of 8.97% was achieved with Tf1 as the cathode interlayer in an inverted polymer solar cell.

Three amino-functionalized fluorene oligomers with different solubility were developed as cathode interfacial materials for inverted polymer solar cells (I-PSCs). By side chain design, we solved the interface layer erosion problem for I-PSCs, and the devices exhibit a power conversion efficiency as high as 8.94%.

Phenanthroline based organic semiconductors (BCP, Bphen, Mphen, and Phen) are used to hybrid with CdS as cathode interlayers in inverted organic solar cells (OSCs). We observed that selecting the polar solvent and hydrophobic interlayers with a diphenyl group could improve the performance of the organic photovoltaic devices. The modification to CdS can effectively improve its electron mobility, film morphology, interfacial contact, and energy level alignment, which finally leads to a significant enhancement of device performance. Through incorporating the CdS–P hybrids (CdS–BCP, CdS–Bphen, CdS–Mphen, and CdS–Phen) as cathode buffer layers, the device PCE (PTB7:PC71BM as the active layer) is greatly improved from 3.09% to 8.36, 7.84, 6.69, and 6.57%, respectively, compared with devices fabricated on the pristine CdS interlayer. These results indicate that the common inorganic semiconductor like CdS can be modified using some organic semiconductors to produce general applicable electron transport layers applied in OSCs. Our work puts forward new insights for the development of new interface modification materials and fabrication of high efficiency devices.

A small-molecule electrolyte based on the popular ethylene diamine tetraacetic acid (EDTA-N) is introduced as an efficient cathode interlayer in inverted polymer solar cells, helping to deliver power conversion efficiency over 9%. The strong dependence of device performance on the external bias suggests that the ion motion plays a critical role in improving the performance of devices with electrolyte interlayers.

Using polyelectrolytes (P3CT-Na) as hole-transporting materials (HTMs), high performance inverted perovskite solar cells with a PCE of 16.6% could be obtained, which was more than 20% improvement compared with those based on the PEDOT:PSS HTM (PCE of 13.7%). The performance improvement can be ascribed to the desirable match of energy levels as well as the better crystalline properties and larger grain size of CH3NH3PbCl3−xIx films on P3CT-Na. Importantly, rather good performance with PCE over 11% is achievable even if the P3CT-Na thickness ranges from 1 nm to 52 nm. Our work indicated the promising applications of polyelectrolyte based HTMs in perovskite solar cells and may provide some insights into the design and synthesis of new HTMs to further improve the device performance.

Three new small organic molecules, I, II and III, consisting of dithienosilole as the central core, bithiophene bridge with different alkyl group substituents, and octyl cyanoacetate or dicyano unit as different end units, have been designed and synthesized. The thermal, optical, electrochemical and photovoltaic properties of these three compounds have been investigated. The solubility, absorption, energy levels and band gaps of these materials were effectively tuned by different alkyl groups substituted on the thiophene unit and/or different electron-withdrawing end groups. Bulk heterojunction solar cells with molecules I–III as electron donors and PC60BM ([6,6]-phenyl-C60-butyric acid methyl ester) as an election acceptor exhibited power conversion efficiencies of 3.27, 2.88 and 3.81% for I, II and III, respectively. All of these solar cells showed very high Voc values of 0.89–0.92 V, and the high Voc is consistent with the low-lying HOMO level of the donor. These compounds also have low LUMO levels which ensure effective charge transfer from the donor to the fullerene acceptor. The structure–photovoltaic property relationships of these donor materials were investigated and discussed.

A highly efficient polymer solar cell was fabricated using a polar fullerene derivative C60 pyrrolidine tris-acid (CPTA) as the cathode buffer layer. By introducing CPTA, the Voc, Jsc and FF were all much enhanced simultaneously. The power conversion efficiency (PCE) was significantly improved to 7.92%, which outperformed the device using Ca/Al as the cathode in our experiment.