Lead iodide perovskite sensitized all-solid-state submicron thin film mesoscopic solar cell with efficiency exceeding 9%

Abstract

We report on solid-state mesoscopic heterojunction solar cells employing nanoparticles (NPs) of methyl ammonium lead iodide (CH(3)NH(3))PbI(3) as light harvesters. The perovskite NPs were produced by reaction of methylammonium iodide with PbI(2) and deposited onto a submicron-thick mesoscopic TiO(2) film, whose pores were infiltrated with the hole-conductor spiro-MeOTAD. Illumination with standard AM-1.5 sunlight generated large photocurrents (J(SC)) exceeding 17 mA/cm(2), an open circuit photovoltage (V(OC)) of 0.888 V and a fill factor (FF) of 0.62 yielding a power conversion efficiency (PCE) of 9.7%, the highest reported to date for such cells. Femto second laser studies combined with photo-induced absorption measurements showed charge separation to proceed via hole injection from the excited (CH(3)NH(3))PbI(3) NPs into the spiro-MeOTAD followed by electron transfer to the mesoscopic TiO(2) film. The use of a solid hole conductor dramatically improved the device stability compared to (CH(3)NH(3))PbI(3) -sensitized liquid junction cells.

Figure 1. Solid-state device and its cross-sectional meso-structure.

(a) Real solid-state device. (b) Cross-sectional structure of the device. (c) Cross-sectional SEM image of the device. (d) Active layer-underlayer-FTO interfacial junction structure.

Figure 2. Diffuse reflectance and UPS spectra for (CH₃NH₃)PbI₃ perovskite sensitizer.

(a) Diffuse reflectance spectrum of the (CH₃NH₃)PbI₃-sensitized TiO₂ film. (b) Transformed Kubelka-Munk spectrum of the (CH₃NH₃)PbI₃-sensitized TiO₂ film. (c) UPS spectrum of the (CH₃NH₃)PbI₃-sensitized TiO₂ film. (d) Schematic energy level diagram of TiO₂, (CH₃NH₃)PbI₃, and spiro-MeOTAD.

Figure 3. Photovoltaic characteristics of (CH₃NH₃)PbI₃ perovskite sensitized solar cell.

(a) Photocurrent density as a function of the forward bias voltage. (b) IPCE as function of incident wavelength. (c) The short circuit photo-current density as function of light intensity.

Figure 4. Effect of TiO₂ film thickness on the key photovoltaic performance parameters.

(a) Short-circuit current density (J_SC), (b) Open circuit voltage (V_OC), (c) fill factor (FF), and (d) power conversion efficiency (PCE).

Figure 5. IS measurements as TiO₂ thickness: red 0.6 µm, blue 1.15 µm and green 1.4 µm.

(a) Dark current during the IS measurements. (b) Recombination resistance extracted from the IS measurements in the dark. (c) Recombination resistance (solid lines) and accompanying capacitance (dashed lines) from IS measurements under illumination. (d) Electron lifetime under illumination.

Figure 6. Femtosecond transient absorbance spectra with λ_exc = 580 nm and WLC probe of a) (CH₃NH₃)PbI₃/Al₂O₃, b) (CH₃NH₃)PbI₃/TiO₂, c) Spiro/(CH₃NH₃)PbI₃/Al₂O_3, and d) Spiro/(CH₃NH₃)PbI₃/TiO₂, recorded at various time delays after excitation (color lines).

Black dashed lines represent the absorbance spectrum of the sample (scaled by a factor –0.01). The wavelengths region around laser excitation (555 – 630 nm) is not shown.

Figure 7. Performance.

Stability of (CH₃NH₃)PbI₃ sensitized solid-state solar cell stored in air at room temperature without encapsulation and measured under one sun illumination.