•Environment-friendly non-halogenated solvents were used to spray-coat the active layers.•Both drying kinetics and charge decay dynamic of spray-processed films were systematically investigated.•Substrate temperatures have a great effect on the spray-coated film morphology.•Spray-processed films with randomly textured surface provide a simple and efficient route to increase light absorption.•Spray-coated ITO-free inverted solar cells processed from non-halogenated solvents were fabricated for the first time.Using spray-coating technique, we successfully fabricated conventional ITO-based and inverted ITO-free polymer solar cells (PSCs) based on a conjugated polymer poly[2,3-bis-(3-octyloxyphenyl) quinoxaline-5,8-diyl-alt-thiophene-2,5-diyl] (TQ1) as the donor and [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) or [6,6] -phenyl-C71-butyric acid methyl ester (PC71BM) as the acceptor. Environment-friendly non-halogenated solvents were used to process the active layers. The influence of substrate temperatures and processing solvents on the photovoltaic performance of the ITO-based TQ1:PC61BM PSCs was systemically investigated. A higher substrate temperature can accelerate the solvent evaporating rate and afford a micro-textured rougher surface, which efficiently reduced light reflectance and enhanced absorption. Furthermore, finer phase separation was observed when using this high substrate temperature, which led to enhanced photocurrent due to the reduced bimolecular recombination. The device performance of spray-processed PSCs using the non-halogenated solvent mixtures was comparable to that of spray-processed PSCs using the halogenated o-dichlorobenzene (oDCB), which demonstrates that the non-halogenated solvents are very promising in spray-processed PSCs. This work sheds new light on developing efficient roll-to-roll compatible spray-coated PSCs with environment-friendly solvents.

•Self-assembly hole injection/transport nanocomposites are applied in deep-blue polymer light-emitting diodes.•Both a finer hole ohmic contact and an increased light outcoupling are achieved.•The device performance is among the best deep-blue PLEDs reported to date.In this study we demonstrate an easy solution-processed highly efficient deep-blue polymer light-emitting diode (PLED) via a simple one-step coating of self-assembly hole injection/transport nanocomposites to achieve both a finer hole ohmic contact and an increased light outcoupling, which is the first time report about both the optical and electrical optimization without necessitating changes in the design or structure of the wide bandgap deep-blue PLEDs themselves. The contact angle and surface energy measurement results demonstrate that triazine-based hole injection molecules can vertically migrate towards the bottom PEDOT:PSS layer to obtain a stable minimum of free energy, resulting in an optimal top-to-bottom HOMO energy level arrangement and an improved hole mobility in deep-blue PLEDs. The random surface nanostructure was formed on top of the hole bilayer, leading to the enhancement of light outcoupling verified by transmittance, transmittance haze and light extraction efficiency. Furthermore, in order to explore the reasons of the hole light scattering formation process, a transient drying monitoring technique is applied to track the drying process of the nanostructure films, revealing this approach effectiveness by easily modifying mixing ratios for obtaining different light outcoupling abilities.Download high-res image (217KB)Download full-size image

Extremely simple one-step coating ITO-free inverted polymer solar cells (IFIPSCs) have been fabricated using a novel film deposition method—doctor blading technique, which is completely compatible with roll-to-roll (R2R) manufacturing. Delamination of the interfacial buffer layer (IBL) from the photoactive mixtures is achieved via a spontaneous vertical self-assembly. The performance of one-step doctor-blading IFIPSCs is primarily influenced by the inherent IBL stratification purity rather than the fine donor/acceptor phase separation for the rigid backbone PTB7 system, which is significantly different from that of the conventional two-step doctor blading devices. The surface energy results strongly demonstrate that the formation of the interfacial layer between the ITO-free cathode and the photoactive layer is significantly controlled by the solvent drying time, which determines the self-assembly quality and can be greatly manipulated from 2700 to 1200 s by different substrate temperatures. It's worth noting that the pure interfacial layer formed at low substrate temperatures improves charge separation and transport, whereas high substrate temperatures limit its growth, leading to the decrease of device performance. The detailed relationship between the self-assembly interfacial layer and the internal resistance and capacitance is revealed by impedance spectroscopy. Encouraging power conversion efficiency (PCE) of 6.56% is achieved from simple one-step doctor-blading ITO-free devices at a very low substrate temperature of 25 °C, which is energy saving and appropriate for industrialized R2R production. In contrast, the highest PCE of 7.11% ever reported for two-step doctor-blading ITO-free IFIPSCs was obtained at a high substrate temperature of 60 °C for achieving a fine morphology without regard to the vertical delamination. Furthermore, for crystalline polymer systems like P3TI with a semi-flexible chain, it requires a higher substrate temperature of 40 °C to mediate the balance of vertical self-assembly stratification of the interfacial buffer layer and photoactive morphology to maximize the device performance.

Correction for ‘Highly efficient and stable blue polymer light emitting diodes based on polysilafluorenes with pendent hole transporting groups’ by Guangrong Jin et al., J. Mater. Chem. C, 2016, DOI: 10.1039/c5tc03665h.

Two homopolymers of triphenylamine and carbazole grafting silafluorenes (PSF-TPA and PSF-Cz) were synthesized and their electroluminescence properties were investigated in this paper. Their carbon analog polyfluorenes with the same substituents were also prepared for comparison. Polysilafluorenes are found to have higher efficiencies and better color purities than the corresponding analog polyfluorenes. Among them, PSF-Cz was found to be a new promising blue-light emitter with an external quantum efficiency of ca. 4.1% and CIE coordinates of (0.16, 0.08), which is among the best deep blue emitters for polymer light-emitting diode (PLED) applications until now. Further study revealed that the silicon atom at the 9-position showed a strong σ conjugation effect and increased the oxidation potential of the final polymer as compared with PF-Cz. The DFT calculation also supports the experimental results. The carrier mobility measurements demonstrate that PSF-Cz has the highest hole mobility and well-balanced hole and electron carriers among them, corresponding to its highest EL efficiency.

In this article we report on a semitransparent polymer solar cell (STPSC) with polymer: fullerene blends sandwiched between a bottom one-dimensional photonic crystal (1DPC) and a top solution-processed highly conductive PEDOT:PSS electrode for light harvesting. The photoelectric parameters of STPSCs are characterized by the measurements of double-face optical transmittance, reflectance, absorption, J–V, EQE, IQE, average visible transmittance, and CIE in conjunction with those of the theoretical calculations based on transfer matrix simulation. The results reveal that the theoretical short-circuit current density (JSC) of 1DPC-STPSC is not sensitive to the active layer thickness due to the relatively weaker microcavity effect compared to that of the conventional opaque PSCs, making the large-area manufacturing process easier. However, it shows a stronger microcavity effect compared to the non-microcavity STPSCs, which is advantageous to light absorption in active blends in the strong absorption band while maintaining visible light transmission in the weak absorption band. The power conversion efficiency of 5.20% and JSC of 12.25 mA cm−2 increased by 37% and 38% respectively when compared with those of the STPSCs without using 1DPC, which is the highest value ever reported for an inverted STPSC with a low-cost highly conductive PEDOT:PSS layer as the light-incident side.

We have developed an ITO/ZnO/CdSe/CdTe:CdSe/CdTe/Au novel device architecture based on solution processed CdTe and CdSe nanocrystals (NCs). The introduced hybrid CdTe:CdSe layer was made by mixing different NCs in solution, which allowed for tailoring the optoelectronic properties of the nanocomposite materials. Our novel devices demonstrated more than 30% improvement in Jsc compared with their bilayer analogue, resulting from suppressed recombination. The champion device showed a 6.25% PCE, which is a record for solution processed CdTe:CdSe p–n junction solar cells with the inverted structure. Most important of all, the devices showed extreme stability after storage for three days when maintained under ambient conditions, and less than 3% degradation was observed in PCE after 50 days of storage.

We report a facile technique of blending a conjugated polymer thieno[3,4-b]thiophene/benzodithiophene (PTB7):[6,6]-phenyl-C71-butyric acid methyl ester (PCBM[70]) active materials with a conjugated interfacial modification polymer poly[(9,9-bis(3′-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)] (PFN) to simplify the coating process and improve the bulk heterojunction (BHJ) polymer solar cell (PSC) performance. The reason for and result of PFN self-organization via a spontaneous vertical delamination onto the ITO surface were investigated by charge transfer state, optical modelling based on transfer matrix formalism, surface energy measurement, scanning Kelvin probe force microscopy and impedance spectroscopy analysis in conjunction with atomic force microscopy and scanning electron microscopy. The relaxed charge transfer state demonstrates that PFN doping has a negligible impact on the donor:acceptor heterojunction interface. The optical simulation of device structures indicates that doping PFN into a BHJ has nearly no influence on the photon absorption profile of the active layer. Very encouraging device performance was achieved in the one-step coating PFN:BHJ PSC with ITO as the cathode, which is comparable to that of the two-step coating PSC. Moreover, for ITO-free inverted PSCs with PEDOT:PSS as the incident light top-electrode, decent device performance can also be obtained, demonstrating the remarkable universality through this facile strategy.

CdTe/CdSe nanocrystal (NC) solar cells with an inverted structure (ITO/ZnO/CdSe/CdTe/Au) have been successfully fabricated by a simple solution process coupled with layer-by-layer sintering techniques. It was found that the device performance is strongly dependent on the annealing strategy, the thickness of the acceptor layer and on the buffer layer of ZnO when the optimal thickness of CdTe is adopted. Without the ZnO buffer layer, a thin film of the CdSe NCs on an ITO substrate shows a rougher morphology, resulting in device shunting. However, when a 40 nm-thick ZnO buffer layer and 60 nm-thick CdSe were employed, the device shows a much higher PCE of 5.81% under device conditions, post-annealing at 340 °C. This value is the highest efficiency ever reported to date for a CdTe/CdSe NC solar cell. Comparing with CdTe/CdSe NC solar cells with the normal device configuration, this device with an inverted structure simultaneously offers good Ohmic contact for carrier collection and efficient harvesting of solar photons in a wide wavelength.

In this study, it has been found that a very fine nanostructure can be realized by mixing 1-chloronaphthalene (CN) – a high-boiling solvent – into a binary chlorobenzene (CB):1,8-diiodooctane (DIO) solvent mixture to form a ternary solvent system. An improvement in energy level alignment is also obtained by doping ICBA into a binary PTB7:PCBM[70] blend, whereby the ternary solute system provides a new pathway for charge transfer from PTB7 to the PCBM[70]:ICBA alloy. This is confirmed by imaging the surface morphology of the active layer using AFM and TEM, monitoring the transient film formation process and measuring the charge transfer states with Fourier transform photocurrent spectroscopy. An encouraging PCE of 7.65% is achieved from the dual ternary system, which is the highest value ever reported for an ITO-free inverted polymer solar cell with a PEDOT:PSS layer as the top semitransparent electrode – a system which is compatible with low-cost large-area roll-to-roll manufacturing.

We present an investigation of deep-blue fluorescent polymer light-emitting diodes (PLEDs) with a novel functional 1,3,5-triazine core material (HQTZ) sandwiched between poly(3,4-ethylene dioxythiophene):poly(styrene sulfonic acid) layer and poly(vinylcarbazole) layer as a hole injection layer (HIL) without interface intermixing. Ultraviolet photoemission spectroscopy and Kelvin probe measurements were carried out to determine the change of anode work function influenced by the HQTZ modifier. The thin HQTZ layer can efficiently maximize the charge injection from anode to blue emitter and simultaneously enhance the hole mobility of HILs. The deep-blue device performance is remarkably improved with the maximum luminous efficiency of 4.50 cd/A enhanced by 80% and the maximum quantum efficiency of 4.93%, which is 1.8-fold higher than that of the conventional device without HQTZ layer, including a lower turn-on voltage of 3.7 V and comparable Commission Internationale de L’Eclairage coordinates of (0.16, 0.09). It is the highest efficiency ever reported to date for solution-processed deep-blue PLEDs based on the device structure of ITO/HILs/poly(9,9-dialkoxyphenyl-2,7-silafluorene)/CsF/AL. The results indicate that HQTZ based on 1,3,5-triazine core can be a promising candidate of interfacial materials for deep-blue fluorescent PLEDs.Keywords: 1,3,5-triazine core; charge balance; deep-blue; fluorescent polymer light-emitting diodes; hole injection layer

•Two different coating methods of doctor blading and spin coating were studied.•The surface tension and viscosity of active solution have effect on film quality.•It is easier to obtain a homogeneous film using doctor blading.•A much longer time is needed for the doctor-blading films to dry.•The longer film drying time allows the crystalline polymer to form larger crystals.Doctor blading is suitable to roll-to-roll process with much little solution wasting and is less studied compared with the mainstream spin coating. In this work, we used a novel polymer blended with two common fullerene derivatives as active solutions. To systemically understand the different coating methods and the different fullerene acceptors on the effect of polymer solar cells (PSCs) photovoltaic performance, the wet active solution physic-chemical properties and variations of the dried active layer characterizations were investigated. It was observed that it is much easier to obtain a homogeneous film from doctor blading compared with spin coating for the polymer: PC71BM solution due to the high surface tension and viscosity. Moreover, the high boiling point additive plays an important role in inhibiting the wet film shrinkage and forming a uniform film. The longer film drying time for the doctor-blading films leads to larger domains than spin coating, thus increases the geminate recombination and results in lower mobilities as well as power conversion efficiencies (PCE). Doctor-blading-processed PSCs with PCE of 4.46% were achieved for P3TI:PC71BM devices, which were comparable to those of spin-coating devices. This work provided valuable suggestions and solutions for the doctor-blading process, especially for crystalline D-A polymer-based devices.

•A four-armed TPA-based molecule with a line molecule as core was synthesized.•A bi-armed TPA-based molecule with the same core was also studied.•The four-armed molecule presents better miscibility with PCBM.•The OSCs based on the four-armed molecule donor show better device performances.A novel four-armed triphenylamine (TPA)-based molecule named (TPATh)4TPA2B with 4,7-bis(4-diphenylaminophenyl)-2,1,3-benzothiadiazole unit as the central building block and triphenylamine-3-dodecylthiophene unit as the arms and a bi-armed TPA-based molecule named (TPATh)2(MTPA)2B with the same central building block and arms as those of (TPATh)4TPA2B were designed and synthesized by Pd-catalyzed Stille reaction. The thermal stability, photophysical and electrochemical properties of these small molecules are studied. Moreover, they are evaluated in solution processed bulk-heterojunction organic solar cells (OSCs). The device performances of the OSCs based on these small molecule donors and [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) were studied. With the same core, the four-armed molecule has the higher absorption and better miscibility with PC71BM than that of bi-armed molecule, while the bi-armed molecule (TPATh)2(MTPA)2B has the higher hole mobility. The power conversion efficiency of the OSCs based on (TPATh)4TPA2B as donor and PC71BM as acceptor is 1.3% with open-circuit voltage 0.71 V.

Two wide band gap four-armed triphenylamine (TPA)-based molecules (SM1 and SM2) with a donor–acceptor–donor structural core and a thiophene (Th) or TPA-Th segment as the arm have been designed and synthesized by use of Stille coupling reaction to further study the relationship between the structure and properties of four-armed triphenylamine-based molecules. The thermal, photophysical, electrochemical and photovoltaic properties of the molecules are studied. To further study the electronic structure of these molecules, time-dependent density functional theory calculations for the resulting small molecules were performed by using the Gaussian 09 program suite. SM2 with the extended arm structures has stronger absorption intensity and better miscibility with commercial PCBM compared with the SM1 molecule. The organic solar cells employing SM2/[6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) as the active layer showed better device performances than that of SM1.

•Four triphenylamine (TPA)-based molecules SM1 with no cyan terminal, SM2, SM3 and SM4 with cyan terminal were prepared.•Cyan terminal has a significant influence on the optical and electronic properties of these small molecules.•The time-dependent density functional theory calculation for the molecules was performed to further study the electronic structure of these molecules.Four triphenylamine (TPA)-based molecules SM1 with no cyan terminal, SM2, SM3 and SM4 with cyan terminal were prepared via Knoevenagel and Stille-coupling reaction to study their optical, electronic and photovoltaic properties. The cyan terminal has a significant influence on the optical and electronic properties of the resulting molecules. The solution processed organic solar cells (OSCs) based on the obtained molecule donors were also fabricated to study their photovoltaic performances. The most efficient OSCs based on SM2 exhibited the power conversion efficiency (PCE) of 1.51% with open-circuit voltage (Voc) of 0.89 V, short current density (Jsc) of 5.80 mA cm−2 and fill factor (FF) of 0.29.

Typically a donor–acceptor (D–A) design strategy is used for engineering the bandgap of polymers for solar cells. However, in this work, a series of alternating D–A1–D–A2 copolymers PnTQTI(F) were synthesized and characterized with oligothiophenes (nT, n = 1, 2, 3) as the donor and two electron-deficient moieties, quinoxaline and isoindigo, as the acceptors in the repeating unit. We have studied the influence of the donor segments with different numbers of thiophene units and the effect of the addition of fluorine to the quinoxaline unit of the D–A1–D–A2 polymers. The photophysical, electrochemical, and photovoltaic properties of the polymers were examined via a range of techniques and related to theoretical simulations. On increasing the length of the donor thiophene units, broader absorption spectra were observed in addition to a sequential increase in HOMO levels, while the LUMO levels displayed very small variations. The addition of fluorine to the quinoxaline unit not only decreased the HOMO levels of the resulting polymers but also enhanced the absorption coefficients. A superior photovoltaic performance was observed for the P3TQTI-F-based device with a power conversion efficiency (PCE) of 7.0%, which is the highest efficiency for alternating D–A1–D–A2 polymers reported to date. The structure–property correlations of the PnTQTI(F) polymers demonstrate that varying of the length of the donor segments is a valuable method for designing high-performance D–A1–D–A2 copolymers and highlight the promising nature of D–A1–D–A2 copolymers for efficient bulk-heterojunction solar cells.

Organic light-emitting diodes were prepared using titanium oxide (TiO2) ultra-thin film by RF magnetron sputtering as the hole buffer layer. The device configuration is ITO/TiO2/N-N′-diphenyl-N-N′-bis(1-naphthyl)-1,1′-biphenyl-4,4′-diamine/tris(8-quinolinolato)-aluminum/LiF/Al. The maximum luminous efficiency for the 1.2 nm TiO2 device is increased by approximately 46% (6.0 cd/A), in comparison with that of the control device (4.1 cd/A). The atomic force microscopy shows that with the insertion of TiO2 buffer layer, the roughness of ITO surface decreases, which is favorable to improve the device luminance and increase the device lifetime. The mechanism behind the enhanced performance is that the TiO2 layer enhances most of the holes injected from the anode and improves the balance of the hole and electron injections.

In this article we report on a semitransparent polymer solar cell (STPSC) with polymer: fullerene blends sandwiched between a bottom one-dimensional photonic crystal (1DPC) and a top solution-processed highly conductive PEDOT:PSS electrode for light harvesting. The photoelectric parameters of STPSCs are characterized by the measurements of double-face optical transmittance, reflectance, absorption, J–V, EQE, IQE, average visible transmittance, and CIE in conjunction with those of the theoretical calculations based on transfer matrix simulation. The results reveal that the theoretical short-circuit current density (JSC) of 1DPC-STPSC is not sensitive to the active layer thickness due to the relatively weaker microcavity effect compared to that of the conventional opaque PSCs, making the large-area manufacturing process easier. However, it shows a stronger microcavity effect compared to the non-microcavity STPSCs, which is advantageous to light absorption in active blends in the strong absorption band while maintaining visible light transmission in the weak absorption band. The power conversion efficiency of 5.20% and JSC of 12.25 mA cm−2 increased by 37% and 38% respectively when compared with those of the STPSCs without using 1DPC, which is the highest value ever reported for an inverted STPSC with a low-cost highly conductive PEDOT:PSS layer as the light-incident side.

CdTe/CdSe nanocrystal (NC) solar cells with an inverted structure (ITO/ZnO/CdSe/CdTe/Au) have been successfully fabricated by a simple solution process coupled with layer-by-layer sintering techniques. It was found that the device performance is strongly dependent on the annealing strategy, the thickness of the acceptor layer and on the buffer layer of ZnO when the optimal thickness of CdTe is adopted. Without the ZnO buffer layer, a thin film of the CdSe NCs on an ITO substrate shows a rougher morphology, resulting in device shunting. However, when a 40 nm-thick ZnO buffer layer and 60 nm-thick CdSe were employed, the device shows a much higher PCE of 5.81% under device conditions, post-annealing at 340 °C. This value is the highest efficiency ever reported to date for a CdTe/CdSe NC solar cell. Comparing with CdTe/CdSe NC solar cells with the normal device configuration, this device with an inverted structure simultaneously offers good Ohmic contact for carrier collection and efficient harvesting of solar photons in a wide wavelength.

In this study, it has been found that a very fine nanostructure can be realized by mixing 1-chloronaphthalene (CN) – a high-boiling solvent – into a binary chlorobenzene (CB):1,8-diiodooctane (DIO) solvent mixture to form a ternary solvent system. An improvement in energy level alignment is also obtained by doping ICBA into a binary PTB7:PCBM[70] blend, whereby the ternary solute system provides a new pathway for charge transfer from PTB7 to the PCBM[70]:ICBA alloy. This is confirmed by imaging the surface morphology of the active layer using AFM and TEM, monitoring the transient film formation process and measuring the charge transfer states with Fourier transform photocurrent spectroscopy. An encouraging PCE of 7.65% is achieved from the dual ternary system, which is the highest value ever reported for an ITO-free inverted polymer solar cell with a PEDOT:PSS layer as the top semitransparent electrode – a system which is compatible with low-cost large-area roll-to-roll manufacturing.

We have developed an ITO/ZnO/CdSe/CdTe:CdSe/CdTe/Au novel device architecture based on solution processed CdTe and CdSe nanocrystals (NCs). The introduced hybrid CdTe:CdSe layer was made by mixing different NCs in solution, which allowed for tailoring the optoelectronic properties of the nanocomposite materials. Our novel devices demonstrated more than 30% improvement in Jsc compared with their bilayer analogue, resulting from suppressed recombination. The champion device showed a 6.25% PCE, which is a record for solution processed CdTe:CdSe p–n junction solar cells with the inverted structure. Most important of all, the devices showed extreme stability after storage for three days when maintained under ambient conditions, and less than 3% degradation was observed in PCE after 50 days of storage.

Correction for ‘Highly efficient and stable blue polymer light emitting diodes based on polysilafluorenes with pendent hole transporting groups’ by Guangrong Jin et al., J. Mater. Chem. C, 2016, DOI: 10.1039/c5tc03665h.

We report a facile technique of blending a conjugated polymer thieno[3,4-b]thiophene/benzodithiophene (PTB7):[6,6]-phenyl-C71-butyric acid methyl ester (PCBM[70]) active materials with a conjugated interfacial modification polymer poly[(9,9-bis(3′-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)] (PFN) to simplify the coating process and improve the bulk heterojunction (BHJ) polymer solar cell (PSC) performance. The reason for and result of PFN self-organization via a spontaneous vertical delamination onto the ITO surface were investigated by charge transfer state, optical modelling based on transfer matrix formalism, surface energy measurement, scanning Kelvin probe force microscopy and impedance spectroscopy analysis in conjunction with atomic force microscopy and scanning electron microscopy. The relaxed charge transfer state demonstrates that PFN doping has a negligible impact on the donor:acceptor heterojunction interface. The optical simulation of device structures indicates that doping PFN into a BHJ has nearly no influence on the photon absorption profile of the active layer. Very encouraging device performance was achieved in the one-step coating PFN:BHJ PSC with ITO as the cathode, which is comparable to that of the two-step coating PSC. Moreover, for ITO-free inverted PSCs with PEDOT:PSS as the incident light top-electrode, decent device performance can also be obtained, demonstrating the remarkable universality through this facile strategy.

Extremely simple one-step coating ITO-free inverted polymer solar cells (IFIPSCs) have been fabricated using a novel film deposition method—doctor blading technique, which is completely compatible with roll-to-roll (R2R) manufacturing. Delamination of the interfacial buffer layer (IBL) from the photoactive mixtures is achieved via a spontaneous vertical self-assembly. The performance of one-step doctor-blading IFIPSCs is primarily influenced by the inherent IBL stratification purity rather than the fine donor/acceptor phase separation for the rigid backbone PTB7 system, which is significantly different from that of the conventional two-step doctor blading devices. The surface energy results strongly demonstrate that the formation of the interfacial layer between the ITO-free cathode and the photoactive layer is significantly controlled by the solvent drying time, which determines the self-assembly quality and can be greatly manipulated from 2700 to 1200 s by different substrate temperatures. It's worth noting that the pure interfacial layer formed at low substrate temperatures improves charge separation and transport, whereas high substrate temperatures limit its growth, leading to the decrease of device performance. The detailed relationship between the self-assembly interfacial layer and the internal resistance and capacitance is revealed by impedance spectroscopy. Encouraging power conversion efficiency (PCE) of 6.56% is achieved from simple one-step doctor-blading ITO-free devices at a very low substrate temperature of 25 °C, which is energy saving and appropriate for industrialized R2R production. In contrast, the highest PCE of 7.11% ever reported for two-step doctor-blading ITO-free IFIPSCs was obtained at a high substrate temperature of 60 °C for achieving a fine morphology without regard to the vertical delamination. Furthermore, for crystalline polymer systems like P3TI with a semi-flexible chain, it requires a higher substrate temperature of 40 °C to mediate the balance of vertical self-assembly stratification of the interfacial buffer layer and photoactive morphology to maximize the device performance.

Two homopolymers of triphenylamine and carbazole grafting silafluorenes (PSF-TPA and PSF-Cz) were synthesized and their electroluminescence properties were investigated in this paper. Their carbon analog polyfluorenes with the same substituents were also prepared for comparison. Polysilafluorenes are found to have higher efficiencies and better color purities than the corresponding analog polyfluorenes. Among them, PSF-Cz was found to be a new promising blue-light emitter with an external quantum efficiency of ca. 4.1% and CIE coordinates of (0.16, 0.08), which is among the best deep blue emitters for polymer light-emitting diode (PLED) applications until now. Further study revealed that the silicon atom at the 9-position showed a strong σ conjugation effect and increased the oxidation potential of the final polymer as compared with PF-Cz. The DFT calculation also supports the experimental results. The carrier mobility measurements demonstrate that PSF-Cz has the highest hole mobility and well-balanced hole and electron carriers among them, corresponding to its highest EL efficiency.