•Two novel β-functionalized D-A-π-A porphyrins are designed and synthesized.•Introduction of additional acceptors in sensitizers influence the optoelectronic properties.•A more electron-withdrawing acceptor is optimal for the enhancement of cell efficiency.The β-functionalized porphyrin containing an additional electron-withdrawing unit, 2,3-diphenylquinoxaline(DPQ) for LP-5 or 2,1,3-benzothiadiazole (BTD) for LP-6 with different electron-withdrawing abilities, between the porphyrin core and the anchoring group and the reference porphyrin dye (LP-4) have been designed and synthesized for DSCs. The influence of the additional electron-withdrawing units on molecular properties as well as photovoltaic performance of the corresponding DSCs was investigated systematically. Compared with LP-4, the introduction of additional electron-deficient unit at the porphyrin β π-linker in LP-5 and LP-6 decreases the lowest unoccupied molecular orbital (LUMO) energy levels, resulting in the broader absorption spectra and significantly improved IPCE spectra in the region 350–500 nm, which ensures the better light-harvesting properties and the higher short-circuit current density (Jsc). On the other hand, the introduction of additional acceptors of LP-5 and LP-6 induces dye aggregation and reduces the lifetime of the charge–separated states, which decreases the open–circuit voltage (Voc). Interestingly, the loss in Voc is overcompensated by the improvement in Jsc. The study provides not only an alternative approach to design novel porphyrin sensitizers, but also an insight into how to manipulate the LUMO energy levels of porphyrin sensitizers via the β-linker modifications for the optimal photovoltaic applications.

Here, a low-temperature solution-processed nickel oxide (NiOx) thin film was first employed as a hole transport layer in both inverted (p-i-n) planar and regular (n-i-p) mesoscopic organic–inorganic hybrid perovskite solar cells (PVSCs). In p-i-n PVSCs, the wetting properties, perovskite morphology, absorption and hole extraction process can be significantly enhanced with a suitable surface treatment, resulting in a significantly increased fill factor (from 0.684 to 0.742) and short circuit current density (from 16.73 to 20.66 mA cm−2). On the basis of the treated NiOx thin film, a promising power conversion efficiency of 15.9% with negligible hysteresis was obtained for inverted planar PVSCs, and 11.8% was obtained for the flexible devices. More importantly, the presynthesized NiOx can be directly deposited on the perovskite film as a top hole transport layer without decomposing the perovskite in n-i-p PVSCs. The resulting n-i-p device shows a five-fold improvement in power conversion efficiency when compared with a hole transport material free device, which indicates that this solution-processed NiOx is promising for all-inorganic charge selection layer based, stable and low cost PVSCs.

Here, we demonstrate an effective low-temperature approach to fabricate a uniform and pinhole-free compact TiO2 layer for enhancing photovoltaic performance of perovskite solar cells. TiCl4 was used to modify TiO2 for efficient charge generation and significantly reduced recombination loss. We found that a TiO2 layer with an appropriate TiCl4 treatment possesses a smooth surface with full coverage of the conductive electrode. Further studies on charge carrier dynamics confirmed that the TiCl4 treatment improves the contact of the TiO2/perovskite interface, facilitating charge extraction and suppressing charge recombination. On the basis of the treatment, we improved the open circuit voltage from 1.01 V of the reference cell to 1.08 V, and achieved a power conversion efficiency of 16.4%.Keywords: charge transport layer; low-temperature; perovskite solar cell; pinhole-free; surface modification

Semitransparent solar cells are highly attractive for application as power-generating windows. In this work, we present semitransparent perovskite solar cells that employ conducting polymer poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) film as the transparent counter electrode. The PEDOT:PSS electrode is prepared by transfer lamination technique using plastic wrap as the transfer medium. The use of the transfer lamination technique avoids the damage of the CH3NH3PbI3 perovskite film by direct contact of PEDOT:PSS aqueous solution. The semitransparent perovskite solar cells yield a power conversion efficiency of 10.1% at an area of about 0.06 cm2 and 2.9% at an area of 1 cm2. The device structure and the fabrication technique provide a facile way to produce semitransparent perovskite solar cells.Keywords: large-area proviskite solar cell; PEDOT:PSS counter electrode; perovskite solar cell; plastic wrap; semitransparent; transfer lamination technique

Three 9,9-dihexyl-9H-fluorene (DHF) functionalized zinc porphyrin dyes (coded as ZZX-N3, ZZX-N4, and ZZX-N5) were designed and synthesized for dye-sensitized solar cells. Then, DHF and benzoic acid were conjugated to the porphyrin ring through triple bonds to act as a spacer to elongate the π-conjugation and as an acceptor for an efficient electron injection, respectively. A bis(9,9-dihexyl-9H-fluorene-7-yl)amine (BFA) and a bis(4-hexylphenyl)amine (BPA) were further linked to DHF to act as electron donors in ZZX-N3 and ZZX-N4, respectively. ZZX-N5 did not have any electron donor and served as a reference. Moreover, ZZX-N3- and ZZX-N4-sensitized cells exhibited broader sunlight absorption than ZZX-N5, and as a result, higher photon-to-electricity efficiency (PCE) (ZZX-N3, 3.83%; ZZX-N4, 4.2%; ZZX-N5, 3.70%) was observed. The results are consistent with well-separated HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital) in ZZX-N3 and ZZX-N4 than in ZZX-N5. However, the overall conversion efficiency of ZZX-N3- and ZZX-N4-sensitized cells was low, which is due to significant dye aggregation induced by the extra long alkyl-chains on the donor groups. This was evidenced by blue and red shifts of the absorption spectra of dye-coated TiO2 films. In addition, the extra long-chains also did not offer better shielding to prevent electron recombination of injected electrons with I3− in electrolyte as revealed by electrochemical impedance spectroscopy. When a co-sensitizer (coded as PBS) was used, a new peak corresponding to the absorption of PBS at 560 nm was observed on the incident photon to charge carrier efficiency (IPCE) spectra; however, the overall photovoltaic performance was not improved due to the significant decrease of dye-loading density of porphyrin dyes, indicating a need to break off the trade-off between dye-loading and light-harvesting.

In this study, new pull–push arylamine-fluorene based organic dyes zzx-op1, zzx-op2, and zzx-op3 have been designed and synthesized for p-type dye-sensitized solar cells (p-DSCs). In zzx-op1, a di(p-carboxyphenyl)amine (DCPA) was used as an electron donor, a perylenemonoimide (PMID) as an electron acceptor, and a fluorene (FLU) unit with two aliphatic hexyl chains as a π-conjugated linker. In zzx-op2 and zzx-op3, a 3,4-ethylenedioxythiophene (EDOT) and a thiophene were inserted consecutively between PMID and FLU to tune the energy levels of the frontier molecular orbitals of the dyes. The structural modification broadened the spectral coverage from an onset of 700 nm for zzx-op1 to 750 nm for zzx-op3. The electron-rich EDOT and thiophene lifted up the HOMO (highest occupied molecular orbital) levels of zzx-op2 and zzx-op3, making their potential more negative than zzx-op1. When three dyes were employed in p-type DSCs with I–/I3– as a redox couple and NiO nanoparticles as hole materials, zzx-op1 exhibited impressive energy conversion efficiency of 0.184% with the open-circuit voltage (VOC) of 112 mV and the short-circuit current density (JSC) of 4.36 mA cm–2 under AM 1.5G condition. Density functional theory calculations, transient photovoltage decay measurements, and electrochemical impedance spectroscopic studies revealed that zzx-op1 sensitized solar cell exhibited much higher charge injection efficiency (90.3%) than zzx-op2 (53.9%) and zzx-op3 (39.0%), indicating a trade-off between spectral broadening and electron injection driving force in p-type DSCs.Keywords: charge injection; fluorene; NiO; organic sensitizer; p-type dye-sensitized solar cells;

•Two novel zinc porphyrin dyes with a bis(9,9-dihexyl-9H-fluorene-7-yl)amine as an electron donor were synthesized.•Dyes displayed broader absorption spectra with an onset ∼700 nm and ∼28 nm red-shift compared to YD2 dye.•Moving long alkyl chains from the porphyrin ring to donor groups increased charge resistance and electron life times.•ZZX-N1 having two 3,5-di-tert-butylphenyl groups in the porphyrin ring gave energy conversion efficiency of 5.78%.Two novel zinc porphyrin dyes (coded as ZZX-N1 and ZZX-N2) with a bis(9,9-dihexyl-9H-fluorene-7-yl)amine (BDFA) as an electron donor and a benzoic acid as an acceptor were designed and synthesized in a donor–π–acceptor configuration for dye-sensitized solar cells. ZZX-N1 with two small 3,5-di-tert-butylphenyl groups on the meso positions of porphyrin ring and ZZX-N2 with two large 2,6-dioctoxylphenyl groups displayed similar absorption spectra with an onset ∼700 nm, and ∼28 nm red-shift was observed when compared to YD2 because of stronger electron donating ability of bis(9,9-dihexyl-9H-fluorene-7-yl)amine (BDFA) than bis(4-hexylphenyl)amine in YD2. ZZX-N1-sensitized cells exhibited higher energy conversion efficiency than ZZX-N2-sensitized device (5.78% vs. 3.61%). The electrochemical impedance study showed higher electron recombination resistance in the interface of TiO2/dye/electrolyte in ZZX-N1-sensitized cell than in ZZX-N2-sensitized cell. The transient decay measurements showed the longer electron lifetime of former than the later. The density functional theory calculations suggested that this could be due to small voids among ZZX-N1 dye molecules on the TiO2 surface, preventing the charge recombination with the redox couple. The results demonstrated the potential of BDFA as an excellent functional group for high efficiency solar cells.

•Conducting polymer PEDOT:PSS film is prepared by transfer lamination.•Plastic wrap is used as the transfer medium for PEDOT:PSS transfer.•The transferred PEDOT:PSS used as the top electrode of organic solar cells.•Solar cells exhibit averaged FF of 0.60 and PCE of 4.0%.We report on the film preparation of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) by transfer lamination using plastic wrap as the transfer medium. Comparing with the commonly used polydimethylsiloxane (PDMS) transfer medium, the plastic wrap is cheaper, easier to access and for mass production. The surface of plastic wrap is less hydrophobic than that of PDMS, aqueous PEDOT:PSS solution with 0.5 wt.% surfactant can wet the plastic wrap well. No plasma or ultraviolet ozone treatment is needed on the plastic wrap prior to the coating of PEDOT:PSS, while plasma treatment is necessary when PDMS is used transfer medium. That simplifies the fabrication process. Organic solar cells with the PEDOT:PSS top electrode transferred using plastic wrap transfer medium exhibit an averaged fill factor of 0.60 and an averaged power conversion efficiency of 4.0%, comparable to that of reference solar cells with PDMS as transfer medium for PEDOT:PSS transfer.Graphical abstract

We report on an experimental study of three organic push–pull dyes (coded as zzx-op1, zzx-op1–2, and zzx-op1–3) featuring one, two, and three fluorene units as spacers between donors and acceptors for p-type dye-sensitized solar cells (p-DSSC). The results show increasing the number of spacer units leads to obvious increases of the absorption intensity between 300 nm and 420 nm, a subtle increase in hole driving force, and almost the same hole injection rate from dyes to NiO nanoparticles. Under optimized conditions, the zzx-op1–2 dye with two fluorene spacer units outperforms other two dyes in p-DSSC. It exhibits an unprecedented photocurrent density of 7.57 mA cm–2 under full sun illumination (simulated AM 1.5G light illumination, 100 mW cm–2) when the I–/I3– redox couple and commercial NiO nanoparticles were used as an electrolyte and a semiconductor, respectively. The cells exhibited excellent long-term stability. Theoretical calculations, impedance spectroscopy, and transient photovoltage decay measurements reveal that the zzx-op1–2 exhibits lower photocurrent losses, longer hole lifetime, and higher photogenerated hole density than zzx-op1 and zzx-op1–3. A dye packing model was proposed to reveal the impact of dye aggregation on the overall photovoltaic performance. Our results suggest that the structural engineering of organic dyes is important to enhance the photovoltaic performance of p-DSSC.

Here, a low-temperature solution-processed nickel oxide (NiOx) thin film was first employed as a hole transport layer in both inverted (p-i-n) planar and regular (n-i-p) mesoscopic organic–inorganic hybrid perovskite solar cells (PVSCs). In p-i-n PVSCs, the wetting properties, perovskite morphology, absorption and hole extraction process can be significantly enhanced with a suitable surface treatment, resulting in a significantly increased fill factor (from 0.684 to 0.742) and short circuit current density (from 16.73 to 20.66 mA cm−2). On the basis of the treated NiOx thin film, a promising power conversion efficiency of 15.9% with negligible hysteresis was obtained for inverted planar PVSCs, and 11.8% was obtained for the flexible devices. More importantly, the presynthesized NiOx can be directly deposited on the perovskite film as a top hole transport layer without decomposing the perovskite in n-i-p PVSCs. The resulting n-i-p device shows a five-fold improvement in power conversion efficiency when compared with a hole transport material free device, which indicates that this solution-processed NiOx is promising for all-inorganic charge selection layer based, stable and low cost PVSCs.

Three 9,9-dihexyl-9H-fluorene (DHF) functionalized zinc porphyrin dyes (coded as ZZX-N3, ZZX-N4, and ZZX-N5) were designed and synthesized for dye-sensitized solar cells. Then, DHF and benzoic acid were conjugated to the porphyrin ring through triple bonds to act as a spacer to elongate the π-conjugation and as an acceptor for an efficient electron injection, respectively. A bis(9,9-dihexyl-9H-fluorene-7-yl)amine (BFA) and a bis(4-hexylphenyl)amine (BPA) were further linked to DHF to act as electron donors in ZZX-N3 and ZZX-N4, respectively. ZZX-N5 did not have any electron donor and served as a reference. Moreover, ZZX-N3- and ZZX-N4-sensitized cells exhibited broader sunlight absorption than ZZX-N5, and as a result, higher photon-to-electricity efficiency (PCE) (ZZX-N3, 3.83%; ZZX-N4, 4.2%; ZZX-N5, 3.70%) was observed. The results are consistent with well-separated HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital) in ZZX-N3 and ZZX-N4 than in ZZX-N5. However, the overall conversion efficiency of ZZX-N3- and ZZX-N4-sensitized cells was low, which is due to significant dye aggregation induced by the extra long alkyl-chains on the donor groups. This was evidenced by blue and red shifts of the absorption spectra of dye-coated TiO2 films. In addition, the extra long-chains also did not offer better shielding to prevent electron recombination of injected electrons with I3− in electrolyte as revealed by electrochemical impedance spectroscopy. When a co-sensitizer (coded as PBS) was used, a new peak corresponding to the absorption of PBS at 560 nm was observed on the incident photon to charge carrier efficiency (IPCE) spectra; however, the overall photovoltaic performance was not improved due to the significant decrease of dye-loading density of porphyrin dyes, indicating a need to break off the trade-off between dye-loading and light-harvesting.