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The surfaces of perovskite films are vulnerable to the moisture in the surroundings, and surface passivation is a widely accessible technique to solve this problem. Here, we report an effective strategy to improve the stability and photovoltaic performance of MAPbI3 perovskite solar cells by surface passivation with Naphthylmethylamine (NMA). The solar cell devices without NMA showed a highest power conversion efficiency (PCE) of 18.4%, while the devices with NMA achieved a highest PCE of 19.4% under the same conditions. The reduced trap density and enhanced recombination resistance are thought to be the main reasons for the improved photovoltaic performance. Moreover, the long-term stability of the passivated solar cell devices was also greatly enhanced. The NMA-treated device maintained 90% of its original PCE after 90 days storage at a relative humidity of 60% and 25 °C, while the device without NMA only maintained 72% of its original PCE under the same conditions.

Molecularly engineered strongly conjugated and rigid hybrid triazatruxene (TAT)-based dyes ZL001 and ZL003 were fabricated as excellent dyes for solid-state dye sensitized solar cells (ssDSSC). Y123 was used as a reference dye. The efficiencies of 5.4%, 6.6% and 6.1% for ZL001, ZL003 and Y123 based solid-state devices are obtained, respectively, with 2,2′,7,7′-tetrakis (N,N-di-p-methoxyphenylamine)-9,9′-spirobifluorene (Spiro-OMeTAD) as hole transporting material. The photovoltaic performance of the TAT-based dye ZL003 was higher than previously published Y123 dye, which possesses a strong push pull conjugated structure. The effects of molecular structure on optical and electrochemical properties, charge extraction kinetics, and photovoltaic performance of the sensitizers were systematically researched. Our results indicate that TAT-based dyes are attractive for application in ssDSSC.

Two-dimensional Ruddlesden-Popper perovskites (2D-RPPs) have attracted attention due to their superior moisture stability. In this study, we prepared and characterized a new group of 2D perovskites with cyclohexane methylamine (CMA+) as a spacer cation. The compounds (CMA)2(MA)n−1PbnI3n+1 (n = 1, 2, 3, and 4) showed high self-assembly (where MA is CH3NH3), which allowed for high-quality films to be deposited through the one-step spin-coating method in ambient air. Hot-casting technique, additives, and glove box were not required in the fabrication process. The bandgaps of this group of compounds can be varied from 2.36 eV for (CMA)2PbI4 (n = 1) to 1.52 eV for MAPbI3 (n = ∞) with increasing n value. Moreover, we found that the thin films of (CMA)2(MA)n−1PbnI3n+1 showed considerable stability in moisture and thermal tests. We successfully inserted these new 2D-RPPs in solar cells, and obtained the best power conversion efficiency of 10.66%, with an open-circuit voltage (Voc) of 1.00 V, and a short-circuit current density (Jsc) of 16.99 mA/cm2 for our first-generation device containing (CMA)2(MA)3Pb4I13 (n = 4). The CMA-based devices exhibited superior long-term stability, the unencapsulated (CMA)2(MA)3Pb4I13 solar cell retained nearly 95% of its initial efficiency when exposed to ambient conditions with a 60% relative humidity for 1500 h.

Two push–pull metal-free sensitizers with 5,11-dihydroindolo[3,2-b]carbazole derivatives as electron-donating groups and 4-(benzo[c][1,2,5]thiadiazol-4-ylethynyl)benzoic acid (BTZ) as electron-withdrawing unit, denoted by SK201 and SK202, were synthesized and used for fabrication of dye-sensitized solar cells (DSSCs). SK202 contains a thienyl group between the donor and acceptor, whereas in SK201 the donor and acceptor are connected directly by a single bond. Introduction of a thienyl group improved the planarity of the dye molecule, broadened the absorption spectrum, enhanced the molar extinction coefficient, increased the dye loading on TiO2, and accelerated interface electron transfer on TiO2. This fine tuning of dye structure improved the performances of DSSCs based on SK202 sensitizers and gave a power conversion efficiency (PCE) of 11.0% (Jsc 16.5 mA cm−2, Voc 932 mV, and fill factor 71.7%), compared with that of 7.2% for SK201, under standard AM1.5G solar irradiation (100 mW cm−2) with a Co(II/III) complex based redox couple.

Two dyes with dithieno[3,2-b:20,30-d] pyrrole (DTP) as the donor (An101 and An102) have been synthesized and characterized. An101 and An102 were applied to dye-sensitized solar cells (DSSCs) and power conversion efficiencies (PCEs) of 8.0% and 9.5% were achieved with the I2−/I3− redox couple, which correspond to open voltages (Voc) of 784 and 690 mV, current densities (Jsc) of 15.1 and 20.0 mA cm−2, the fill factors of 67.2% and 68.7%, respectively, under AM1.5G irradiation. It is worth noting that the different connection locations of the donors with the π-bridge result in different PCEs. An102 has a higher Jsc owing to its high molar extinction coefficient and small torsion angle, which increase the light-harvesting ability and coplanarity. An101 has a higher Voc owing to introduction of the alkoxybenzene group, which can effectively suppress recombination with the electrolyte and dye. By scanning with different bias voltages with electrochemical impedance spectroscopy, the reason for the high voltage of the An101 dye is up-shift of the TiO2 conduction-band edge and elongated electron lifetimes. However, the main reason for the relatively high PCE of the An102 dye is the coplanarity, which results in good long-term stability.

P-type doping is a rational strategy for the enhancement of hole transporting properties of the organic semiconductors as well as the device performance of organic photo-electric devices. We originally introduce a stable and solution processed p-type dopant based on N-oxoammonium salts termed 2,2,6,6-tetramethyl-1-oxopiperidinebromide salt (TEMPO-Br) for 2,2′,7,7′-tetrakis(N, N-di-p-methoxyphenyl-amine)9,9′-spirobifluorene (Spiro-OMeTAD) based solid state dye sensitized solar cells (ssDSC). By introducing TEMPO-Br doped Spiro-OMeTAD and a commercialized D-π-A sensitizer into ssDSCs, a promising device performance of 6.83% is achieved under simulated AM 1.5G solar irradiation (100 mW cm−2), which is significantly better than the control devices (∼1.7 times). The doping effect of TEMPO-Br on the photophysical and electrochemical properties of Spiro-OMeTAD, solid state device performance, cationic dye regeneration kinetics and preliminary long-term stability have been systematically investigated. This work indicates a potential application of N-oxoammonium salts as chemical P-type dopants for triphenylamine based hole transporting materials in solid state photo-electric devices.

Colloidal quantum dot (CQD) solar cells with a ZnO/PbS-TBAI/PbS-EDT/carbon structure were prepared using a solution processing technique. A commercially available carbon paste that was processed at low-temperatures was used as a counter electrode in place of expensive noble metals, such as Au or Ag, which are used in traditional PbS CQD solar cells. These CQD solar cells exhibited remarkable photovoltaic performance with a short circuit density (Jsc) of 25.6 mA/cm2, an open circuit voltage (Voc) of 0.45 V, a fill factor (FF) of 51.8% and a power conversion efficiency (PCE) as high as 5.9%. A reference device with an Au counter electrode had a PCE of 6.0%. The PCE of the carbon-containing CQD solar cell remained stable for 180 days when tested in ambient atmosphere, while the PCE of the Au-containing CQD solar cell lost 48.3% of its original value. Electrochemical impedance spectroscopy (EIS) demonstrated that holes within the PbS CQD were effectively transported to the carbon counter electrode.