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Abstract: Mixed alloy Cu–In–Ga precursors were deposited from Cu–Ga alloy and Indium targets by the DC magnetron co-sputtering method. There were four crystallization phases, In, CuIn2, Cu11In9 and Cu3Ga, identified in the precursor after deposition. A large grain-size CIGS film was achieved by controlling the annealing period for selenization and utilizing a two-stage selenization process for secondary crystallization during rapid thermal annealing process. As the annealing temperature increased, the phase transitions moved toward the Cu-rich inter-metallic phases. In addition, the phase transition, stoichiometric ratio and surface-morphology were modified by Ar-ion plasma etching process of the precursors. The results show that after the ion etching process, the precursors can be transferred into a single Cu11In9 crystallization phase and the number of crevices increased due to the soft texture of indium on the surface of the precursors. Finally, CIGS films with good crystalline properties were achieved after a suitable selenization process of only 1-stage. [Copyright &y& Elsevier]

Comprehensive studies were carried out to explore the roles of phenyl-C 61 -butyric acid methyl ester (PCBM) thin films in inverted-type CH 3 NH 3 PbI 3 (MAPbI 3 ) based photovoltaics, including the surface morphologies, transmittance spectra, photoluminescence spectra, X-ray diffraction (XRD) patterns, Raman scattering spectra and thin-film residual stress analysis. The reduction in the photoluminescence line width indicates that the crystallinity of the MAPbI 3 thin film can be increased by covering it with the PCBM thin film. The XRD patterns and Raman scattering spectra show a reduction in the compressive stress of MAPbI 3 thin film when covered by the PCBM thin film. In addition, it is noted that the residual stress at the contact interface between the hydrophilic MAPbI 3 and the hydrophobic PCBM can be ignored as confirmed by the results obtained with a home-made Twyman-Green interferometer. Consequently, the superior optoelectronic properties of the perovskite materials, as well as the use of a multifunctional fullerene-based thin film as the capping layer allow for the high-efficiency perovskite photovoltaics. [ABSTRACT FROM AUTHOR]

A series of nonpolar antisolvents (chlorobenzene, bromobenzene, iodobenzene and toluene) were used to assist in the formation of smooth and crystalline CH 3 NH 3 PbI 3 thin films by a one-step spin-coating method. The structural, optical and excitonic characteristics of the resultant CH 3 NH 3 PI 3 thin films were analyzed using an atomic-force microscope, X-ray diffractometer, absorbance spectrum, photoluminescence (PL) spectrum, time-resolved PL and temperature-dependent PL. The properties of the CH 3 NH 3 PbI 3 thin films are dependent on the relative polarity and boiling point of the nonpolar antisolvents used in the washing treatment process. The interplay between nucleation (relative polarity) and crystal growth (boiling point) during the formation of CH 3 NH 3 PbI 3 thin films influences the short-circuit current density (J SC ) and power conversion efficiency (PCE) of the corresponding solar cells. The experimental results demonstrate that iodobenzene can be substituted for toluene as a more efficient antisolvent in the washing treatment process during the fabrication of CH 3 NH 3 PbI 3 thin films. In addition, it is predicted that the J SC and PCE can be further improved by increasing the crystallinity of the CH 3 NH 3 PbI 3 thin film. [ABSTRACT FROM AUTHOR]

A comprehensive study was carried out to understand the influence of organic cations on high-performance CH 3 NH 3 PbI 3 based photovoltaics. Scanning electron microscope, X-ray diffractometer, Hall measurement, absorbance spectrum, photoluminescence (PL) spectrum and nanosecond time-resolved PL measurements were used to explore the structural, electrical, optical and excitonic characteristics of CH 3 NH 3 PbI 3 thin films fabricated under different thermal annealing temperatures from 60 °C to 140 °C. The decrease in the open-circuit voltage ( V OC ) with an increase in the thermal annealing temperature can be explained as due to the reduced work function of the CH 3 NH 3 PbI 3 thin film. The short-circuit current density ( J SC ) of the CH 3 NH 3 PbI 3 based photovoltaics is dependent on the efficiencies of light absorption and carrier collection, which results in an optimized J SC when the thermal annealing temperature is 120 °C. The atomistic interaction between the organic cations and Pb–I framework strongly influences the absorbance of CH 3 NH 3 PbI 3 thin films, as confirmed by the libration of CH 3 NH 3 cations shown by Raman scattering spectroscopy. In addition, the experimental results indicate that the power conversion efficiency can be further improved when the absorption strength of the CH 3 NH 3 PbI 3 thin film and the energy-level alignment of each photovoltaic layer are simultaneously fulfilled. [ABSTRACT FROM AUTHOR]

The open-circuit voltage of CH 3 NH 3 PbI 3 based photovoltaics was enhanced from 0.77 V to 0.9 V, which resulted in an improvement of the average power conversion efficiency from 5.63% to 11.74% achieved by tuning the work function of the poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) hole transport layer. The higher work function of the PEDOT:PSS (1:20 wt%) thin film, as compared to the PEDOT:PSS (1:6 wt%) and PEDOT:PSS (1:2.5 wt%) thin films, was observed using photoelectron spectrometer. The carrier density of PEDOT was obtained by analyzing the transmittance spectrum of PEDOT:PSS/glass with the transfer matrix method. The Drude model can be used to explain the increased work function of the PEDOT:PSS thin film obtained by decreasing the ratio of PEDOT to PSS. The increased carrier density of the PEDOT in PEDOT:PSS thin films originated from conformational changes in the PEDOT chains as confirmed by Raman scattering spectroscopy. [ABSTRACT FROM AUTHOR]

Transmittance spectra, atomic-force microscopic images, energy-dispersive X-ray spectra and droplet contact angle images show that a facile wet etching process can be used to manipulate the thickness, surface roughness, surface chemical composition and surface wettability of the indium-tin oxide (ITO) thin films, which influences the molecular packing structure of the P3CT-Na thin films and thereby dominating the crystal quality of the CH 3 NH 3 PbI 3 (MAPbI 3) thin films. The power conversion efficiency (PCE) of the P3CT-Na based MAPbI 3 solar cells can be improved from 17.02% to 19.35% by increasing the Sn/In concentration ratio of the ITO thin films from 0.36 to 0.47 with a facile wet etching process at a constant temperature of 40 °C. It is noted that the PCE of the optimal solar cell decreases slowly toward a stable PCE of 16% for more than 60 days under moderate environment conditions (55 ± 10 RH%). • Surface properties of the ITO/glass substrates can be varied by the wet etching process. • The contact quality at the P3CT-Na/ITO interface can be improved. • The contact quality at the MAPbI3/P3CT-Na interface can be improved. • After 60 days, the PCE slowly decreased from 19.35% to 16.03%. [ABSTRACT FROM AUTHOR]

—The structural, optical and excitonic characteristics of urea doped CH 3 NH 3 PbI 3 (MAPbI 3) multi-crystalline thin films were investigated by using the X-ray diffraction patterns, atomic-force microscopic images, absorbance spectra, photoluminescence (PL) spectra and Raman scattering spectra. The surface-sensitive Raman scattering spectra show that the urea small molecules are mainly distributed in the top region of the MAPbI 3 thin films and thereby effectively passivating the electron-poor defects (interfacial MA cations) of MAPbI 3 thin films. Besides, the thermal annealing temperature and the concentration of urea additive both strongly influence the formation of MAPbI 3 thin films, which dominates the photovoltaic performance. The use of 5-wt% urea can increase the open-circuit voltage (V OC) and short-circuit current density (J SC) of the MAPbI 3 solar cells from 0.88 V to 19.75 mA/cm2 to 0.94 V and 22.97 mA/cm2, respectively. In addition, the reduced current hysteresis in the J-V curves of the MAPbI 3 solar cells can be explained as due to the effective defect passivation in the top region of the MAPbI 3 thin film by the oxygen-donors of the urea small molecules. Image 1 • The optoelectronic properties of urea-doped MAPbI 3 thin films are investigated. • The 5-wt% urea-doped MAPbI 3 thin film has the disk-like shaped grains. • The urea small molecules are mainly distributed in the top region of MAPbI3 thin films. • The V OC and J SC of MAPbI3 solar cells are simultaneously increased by using the urea additive. [ABSTRACT FROM AUTHOR]