A high-quality perovskite film with interconnected perovskite grains was obtained by incorporating terephthalic acid (TPA) additive into the perovskite precursor solution. The presence of TPA changed the crystallization kinetics of the perovskite film and promoted lateral growth of grains in the vicinity of crystal boundaries. As a result, sheet-shaped perovskite was formed and covered onto the bottom grains, which made some adjacent grains partly merge together to form grains-interconnected perovskite film. Perovskite solar cells (PSCs) with TPA additive exhibited a power conversion efficiency (PCE) of 18.51% with less hysteresis, which is obviously higher than that of pristine cells (15.53%). PSCs without and with TPA additive retain 18 and 51% of the initial PCE value, respectively, aging for 35 days exposed to relative humidity 30% in air without encapsulation. Furthermore, MAPbI3 film with TPA additive shows superior thermal stability to the pristine one under 100 °C baking. The results indicate that the presence of TPA in perovskite film can greatly improve the performance of PSCs as well as their moisture resistance and thermal stability.Keywords: efficiency; interconnection; perovskite solar cells; stability; terephthalic acid;

•Ordered porous hierarchical TiO2 (hier-TiO2) was synthesized by sintering MOFs.•The scaffold of scattered distribution was prepared by hier-TiO2 nanostructures.•The crystallization of perovskite was controlled due to ordered porous hier-TiO2.•Grains with enlarged sizes were formed due to scaffold of scattered distribution.•PSCs with hier-TiO2 scaffold show higher efficiency and better stability.A type of quasi-mesoscopic perovskite solar cells (QM-PSCs) with porous hierarchical TiO2 (hier-TiO2) nanostructures of scattered distribution as scaffold was investigated. The porous hier-TiO2 nanostructures were synthesized by sintering MIL-125(Ti) of metal-organic frameworks (MOFs) at 500 °C in air and which were partly inherited from the ordered porosity of MIL-125(Ti). The ordered hier-TiO2 nanostructures were scattered on compact TiO2 layer to form a quasi-mesoscopic scaffold of scattered distribution, which can offer enough growth space for perovskite grains and promote the ordered growth of perovskite grains. The QM-PSCs shows a power conversion efficiency (PCE) of 16.56%, much higher than PCE (11.38%) of PSCs with conventional small TiO2 nanoparticles (npt-TiO2) as scaffold and PCE (6.07%) of planar PSCs with compact TiO2 layer. The PCEs of PSCs with hier-TiO2 and npt-TiO2 remain 47% and 22% of the initial PCE values aging for 30 days in air, indicating that PSCs with hier-TiO2 scaffold shown better stability and moisture resistance. The enhanced performance of QM-PSCs is primarily attributed to the superior wettability quasi-mesoscopic scaffold with ordered porous hier-TiO2 nanostructures, which help to form the high quality perovskite film with better crystillinity and less pin-holes, and improve the contact properties between perovksite and electron transport layer.Download high-res image (114KB)Download full-size image

As a hole transport layer, PEDOT:PSS usually limits the stability and efficiency of perovskite solar cells (PSCs) due to its hygroscopic nature and inability to block electrons. Here, a graphene-oxide (GO)-modified PEDOT:PSS hole transport layer was fabricated by spin-coating a GO solution onto the PEDOT:PSS surface. PSCs fabricated on a GO-modified PEDOT:PSS layer exhibited a power conversion efficiency (PCE) of 15.34%, which is higher than 11.90% of PSCs with the PEDOT:PSS layer. Furthermore, the stability of the PSCs was significantly improved, with the PCE remaining at 83.5% of the initial PCE values after aging for 39 days in air. The hygroscopic PSS material at the PEDOT:PSS surface was partly removed during spin-coating with the GO solution, which improves the moisture resistance and decreases the contact barrier between the hole transport layer and perovskite layer. The scattered distribution of the GO at the PEDOT:PSS surface exhibits superior wettability, which helps to form a high-quality perovskite layer with better crystallinity and fewer pin holes. Furthermore, the hole extraction selectivity of the GO further inhibits the carrier recombination at the interface between the perovskite and PEDOT:PSS layers. Therefore, the cooperative interactions of these factors greatly improve the light absorption of the perovskite layer, the carrier transport and collection abilities of the PSCs, and especially the stability of the cells.

•Self-formed AlOx at Al/MoO3 interface improve built-in field of polymer solar cells.•Too Thick AlOx increase Rs, which reduce efficiency and stability of Al based cells.•Thickness of AlOx interlayer self-formed at AgAl/MoO3 interface can be controlled.•Dense and right thick AlOx improve PCE and longtime stability of AgAl based PSCs.•AZO instead of ZnO as ETL helps to improve efficiency and UV-resistance of PSCs.Al as a cheap and air-stable metal material has been widely applied to polymer solar cells (PSCs) as an efficient electrode. However, there are few care whether Al is a right electrode in PSCs for longtime stability. The inverted PSCs with the structure of ITO/ZnO/PTB7-Th:PC71BM/MoO3/Metal electrode were fabricated and the performance and stability of inverted PSCs with Al and AgAl electrodes were investigated. PSCs with AgAl electrode got the highest PCE value of 9.3% without aging. While the PCE of PSCs with Al electrode can be gradually improved and reach the highest value of 7.8% after aging for 36 h, which is attributed to the formation of AlOx interlayer at the interface of MoO3/Al. PSCs with AgAl electrode still retained 69% of the initial PCE value and got 6.6% of PCE aging for 796 days, showing amazing stability. However, PSCs with Al electrode was dropped to 3.7% of PCE aging for 796 days due to the continuously increased thickness of AlOx interlayer, which can greatly increase the series resistance of cells. PSCs with AgAl electrode can be further improved and reach 10.2% of PCE using AZO (Al doped ZnO) instead of ZnO and show better UV-light resistance. The enhanced stability of PSCs with AgAl electrode is attributed to the dense and limited thick AlOx interlayer self-formed at the MoO3/AgAl interface due to the low content of Al. Our results demonstrated that Ag alloy electrode such as AgAl is a good strategy to accurately control the thickness of the metal oxidation interlayer, which can overcome the disadvantage of Al electrode and greatly improve the longtime stability of devices.Download high-res image (153KB)Download full-size image

The performance characteristics of polymer solar cells (PSCs) incorporated with AgAl and Ag nanostructures and MoO3 spacer layers were investigated. The power conversion efficiency (PCE) of PSCs is sensitive to the nominal thicknesses of the AgAl nanostructures and the MoO3 spacer layer. The PCE of a PSC with a 3-nm-thick layer of AgAl nanostructures and a 1-nm-thick MoO3 isolation layer reached 9.79%, which is higher than the PCE (8.55%) of the reference PSC without metal nanostructures. Compared to PSCs with Ag nanostructures, PSCs with AgAl nanostructures showed better stability and still retained 60% of their initial PCE values after aging for 120 days in air without encapsulation. The enhanced stability of the PSCs is attributed to the formation of AlOx, which can inhibit the diffusion of Ag atoms into the neighboring layer. The localized surface plasmonic resonance (LSPR) effect of AgAl nanostructures was retained by inserting an only 1-nm-thick MoO3 spacer layer between the metal nanostructures and the metal electrode. Our work has demonstrated that using AgAl alloy instead of Ag as plasmonic nanostructures is a better strategy for improving the performance of PSCs, especially in terms of the stability of the cells.Keywords: AgAl alloy; local surface plasmonic resonance; metal nanoparticles; polymer solar cells; stability

The performance and air stability of inverted polymer solar cells (PSCs) were greatly improved using a combination of LiF-modified ITO cathode and a MoO3/AgAl alloy anode. The power conversion efficiency (PCE) of PSCs with AgAl contact reached 9.4%, which is higher than that of the cells with Ag (8.8%) and Al electrode (7.6%). The PCE of AgAl-based PSCs can further increase up to 10.3% through incorporating an ultrathin LiF-modified ITO. AgAl-based cells also exhibit a superior stability compared to the cells with Ag and Al contacts. PCE of the AgAl-based cells without encapsulation remains 78% of its original value after the cells were aged for 380 days in air. The presence of a LiF-modified ZnO interlayer between ITO and the organic active layer improves the charge collection. The improvement in PCE and stability of the AgAl-based cells is primarily attributed to the formation of AlOx at the MoO3/AgAl interface, preventing Ag diffusion and improving the built-in potential across the active layer in the cells.Keywords: AgAl alloy; electrodes; high efficiency; LiF interlayer; MoO3; polymer solar cells; stability; ZnO

•Perovskite solar cells with different cathode of Al, Ag and AgAl were fabricated.•Cells with AgAl alloy retained 90% of the initial PCE values after aging 48 h.•Cells with AgAl kept the initial Voc during aging 360 h, showing amazing stability.•The superior stability of cells with AgAl is attributed to the formation of AlOX.•AlOX formed boosts electron extraction and inhibits moisture encroachment.The progresses made in emerging perovskite solar cells, a promising alternative photovoltaic technology to the conventional solar cells, have quickly set the power conversion efficiency (PCE) record of 20%. Apart from the high PCE, the stability of perovskite solar cells is another important issue for them to be commercially viable. To investigate the impact of electrodes on the stability of the perovskite solar cells, cells with a structure of ITO/PEDOT:PSS/CH3NH3PbI3/PCBM/Cathode, having different cathode contacts of Al, Ag and AgAl alloy, were fabricated. The cells with an AgAl alloy cathode reached a PCE of 11.76%, which is slightly higher than that (11.45%) of the structurally identical cells with Ag contact, much higher than that for the ones with Al electrode (7.95%). The stable open-circuit voltage (VOC) of cells having an AgAl contact was demonstrated, with almost no change in the VOC after 360 h aging under a relative humidity of 10% in air. However, there is an obvious drop in the VOC of the structurally identical perovskite cells with Ag cathode, e.g., an 85% decrease from its initial VOC value for cells aged under the same condition. The enhancement in the PCE of cells with AgAl cathode is attributed to the formation of AlOX, which can improve built-in potential in the cell and allow an effective electron extraction at the PCBM/AgAl cathode interface. An interfacial AlOX interlayer could be formed at the interface between PCBM and AgAl contact during thermal evaporation and aging. The presence of the interfacial AlOX interlayer helps to prevent the diffusion of the Ag atoms into the active layer, to improve the adhesion of the metal contact on PCBM and also to avoid moisture encroachment.

•ZnGa2O4:Eu3+ nanophosphor is used in mesoporous TiO2 of perovskite solar cells.•The nanophosphor improves the light absorption and exciton generation rate.•The nanophosphor increases the cell photocurrent and efficiency.•An extremely high photocurrent density of 25.02 mA cm−2 is achieved.ZnGa2O4:Eu3+ nanophosphor was synthesized through a hydrothermal method and used as an effective light down-shifting/converting material in mesoporous TiO2 layer of perovskite solar cells (PSCs). The nanophosphor can convert the high energy incident photon into the photon(s) with lower energy, which can excite CH3NH3PbI3 to generate more photo generated electron–hole pairs, and thus promote the incident light use ratio and increase the power conversion efficiency (PCE) of PSCs. After the incorporation of suitable amount of ZnGa2O4:Eu3+ into PSCs, the cell PCE is increased to 13.80% with a photocurrent density of 23.68 mA cm−2 and a highest PCE of 14.34% with a photocurrent density of 25.02 mA cm−2 is achieved, much higher than those of the cell without ZnGa2O4:Eu3+ (PCE of 10.67% and photocurrent density of 20.2 mA cm−2). The enhanced photovoltaic performance by incorporating the nanophosphor into PSCs should be ascribed to the increased incident light use ratio and improved exciton generation rate.

•Thermal stability of GZO/AgTi/AZO(GATG) was improved by doping Ti into Ag film.•Enhanced thermal stability is attributed to the formation of TiOX in Ag film.•GATG substituting ITO as electrode were used in inverted polymer solar cells.•PCE of PSCs with GATG reached 9.2%, comparable to PCE of PSCs with ITO electrode.•PSCs with GATG compared to ITO electrode show better UV durability.The optical and electrical properties of GZO/AgTi/AZO (GATG) multilayer transparent conducting films fabricated by magnetron sputtering method were investigated. The sheet resistance and maximum optical transmittance of GATG films are 5 Ω/sq and 86%, respectively. The sheet resistance of GATG still retains stable under annealing at 400 °C, which shows better thermal stability compared to GZO/Ag/AZO (GAG) film. The enhanced thermal stability of GATG is attributed to the formation of TiOX in Ti doped Ag nanostructure film, which can inhibit Ag atom diffusion and aggregation. PTB7-TH:PC71BM based inverted polymer solar cells (PSCs) with GATG electrode gave PCE of 9.20%, which is comparable to PCE (9.23%) of the control PSCs with ITO electrode. The PCE of PSCs with GATG and ITO electrodes respectively remain 59% and 23% of the original PCE values after UV exposure for 20 min with relativize humidity of 68% in air, indicating that PSCs with GATG show better UV durability. Our results suggest that GATG as an alternative to ITO electrode can obtain efficient inverted PSCs and have stronger anti-UV ability due to its low UV transparency.

•Au and LiF layers were inserted into ITO/ZnO interface for electron extraction.•PSCs showed a 40% increase in PCE with an optimal Au/LiF interlayer.•Au/LiF-modified ZnO interlayer improves the charge collection and PCE of PSCs.•Plasmon resonance effect of Au islands also contributed to the improvement in PCE.•PSCs with LiF modified ZnO layer compared to bare ZnO layer improved cell lifetime.The performance enhancement of inverted polymer solar cells (PSCs), based on the blend system of regioregular poly(3-hexylthiophene) and [6,6]-phenyl C61-butyric acid methylester, due to incorporating ultrathin Au and LiF interlayer between the front transparent indium tin oxide and a ZnO electron transporting layer was analyzed. The results reveal that a 40% increase in PCE, e.g., from 2.62% to 3.67%, was observed for PSCs made with an optimal Au/LiF interlayer as compared to the one having a bare ZnO electron transporting layer. The presence of Au/LiF-modified ZnO interlayer between ITO and the organic layer helps to improve the charge collection. The absorption enhancement arising from the plasmon resonance of Au nanostructures also contributed to the improvement in PCE. It is shown that PSCs with LiF incorporated ZnO electron transporting layer allow improving cell lifetime, demonstrating <50% decrease in PCE compared to that of the ones with a bare ZnO interlayer after 240 day aging test for cells without encapsulation in air.

We report efficient mixed halide perovskite solar cells using thermally evaporated Ag or AgAl alloy layers as back electrodes. The properties of AgAl alloy and Ag films deposited on a hole-transport material layer for use in CH3NH3PbI3−xClx solar cells were investigated. The influence of the distance between the metal source and the sample on the performance of the solar cells was determined. The cell with an Ag layer deposited at a distance of 20 cm displayed a power conversion efficiency (PCE) of 5.49%. When the Ag layer was deposited at a distance of 30 cm, the resulting device achieved a 46.8% enhancement in PCE compared to the cell with the Ag prepared at 20 cm. Furthermore, the AgAl alloy based perovskite solar cell accomplished a 37.3% enhancement in PCE compared to the optimized Ag electrode. The fabricated AgAl alloy perovskite cells show a fill factor of 59.6%, open-circuit voltage of 0.88 V, short-circuit current density of 21.11 mA cm−2, yielding an overall efficiency of 11.07%. The AgAl alloy layer exhibited high optical reflectivity and good adhesion on the hole-transport material layer compared to a layer of Ag. The PCE enhancement mechanisms are discussed. Our work has demonstrated that AgAl is a promising back electrode material for high-efficiency perovskite solar cells.

ZnO thin film was fabricated on tin-doped indium oxide electrode as an electron selective layer of inverted polymer solar cells using magnetron sputtering deposition. Ionic liquid-functionalized carbon nanoparticles (ILCNs) film was further deposited onto ZnO surfaces by drop-casting ILCNs solution to improve interface properties. The power conversion efficiency (PCE) of inverted polymer solar cells (PSCs) with only ZnO layer was quickly decreased from 2.7% to 2.2% when the thickness of ZnO layer was increased from 15 nm to 60 nm. However, the average PCE of inverted PSCs with ZnO layer modified with ILCNs only decreased from 3.5% to 3.4%, which is comparable to that of traditional PSCs with poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) anode buffer layer. The results suggested that the contact barrier between ZnO layer and poly(3-hexylthiophene) and phenyl-C61-butyric acid methylester (P3HT:PCBM) blended film compared to ZnO bulk resistance can more significantly influence the performance of inverted PSCs with sputtered ZnO layer. The vanishment of negative capacitive behavior of inverted PSCs with ILCNs modified ZnO layer indicated ILCNs can greatly decrease the contact barrier of ZnO/P3HT:PCBM interface.

•ZnO electron selective layers were deposited by magnetron sputtering.•Performance of polymer solar cells (PSCs) is closely related to ZnO film thickness.•ZnO surface roughness was gradually increased with increasing ZnO film thickness.•Intensive roughness of ZnO layer results in deteriorated performance of PSCs.The performance of inverted polymer solar cells (PSCs) was investigated using ZnO layer as an electron selective layer ranging from 15 nm to 60 nm thickness by magnetron sputtering deposition. The average power conversion efficiency (PCE) of inverted poly(3-hexylthiophene) and phenyl-C61-butyric acid methylester (P3HT:PCBM) based PSCs with 15 nm and 30 nm thickness ZnO layer respectively reaches 3.63% and 3.45%, which is comparable to that of traditional PSCs with poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) anode buffer layer. The deteriorated PCE 2.65% of PSCs with 60 nm ZnO layer is attributed to the intensive surface roughness of ZnO layer by atomic force microscopy images. The increasing PCE 3.44% of PSCs with ionic liquid-functionalized carbon nanoparticles (ILCNs) modified 60 nm ZnO layer suggested that the interface contact at the interface of ZnO/P3HT:PCBM was significantly improved by ILCNs modification. The always positive capacitive behavior of PSCs with 15 nm, 30 nm and ILCNs modified 60 nm ZnO layer further demonstrated their superior interface contact at ZnO/P3HT:PCBM compared to PSCs with 60 nm ZnO layer due to its negative capacitance.

Magnetic tunnel junctions (MTJs) based on MgO barrier have been fabricated by sputtering single crystal MgO target and metal Mg target, respectively, using magnetic sputtering system Nordiko 2000. MgO barriers have been formed by a multi-step deposition and natural oxidization of Mg layer. Mg layer thickness, oxygen flow rate and oxidization time were adjusted and the tunnel magnetoresistance (TMR) ratio of optimal MTJs is over 60% at annealing temperature 385°. The (001) MgO crystal structure was obtained when the separation distance between MgO target and substrate is less than 6 cm. The TMR ratio of most MgO based MTJs are over 100% at the separation distance of 5 cm and annealing temperature 340°C. The TMR ratios of MTJs are almost zero when the separation distance ranges from 6 to 10 cm, due to the amorphous nature of the MgO film.