Potassium-doped organometal halide perovskite solar cells (PSCs) of more than 20% power conversion efficiency (PCE) without I-V hysteresis were constructed. The crystal lattice of the organometal halide perovskite was expanded with increasing of the potassium ratio, where both absorption and photoluminescence spectra shifted to the longer wavelength, suggesting that the optical band gap decreased. In the case of the perovskite with the 5% K+, the conduction band minimum (CBM) became similar to the CBM level of the TiO2-Li. In this situation, the electron transfer barrier at the interface between TiO2-Li and the perovskite was minimised. In fact, the transient current rise at the maximum power voltages of PSCs with 5% K+ was faster than that without K+. It is concluded that stagnation-less carrier transportation could minimise the I-V hysteresis of PSCs.
Frequently observed high V loss in tin-lead mixed perovskite solar cells is considered to be one of the serious bottle-necks in spite of the high attainable Jsc due to wide wavelength photon harvesting. An amicable solution to minimize the V loss up to 0.50 V has been demonstrated by introducing an n-type interface with spike structure between the absorber and electron transport layer inspired by highly efficient Cu(In,Ga)Se solar cells. Introduction of a conduction band offset of ∼0.15 eV with a thin phenyl-C61-butyric acid methyl ester layer (∼25 nm) on the top of perovskite absorber resulted into improved V of 0.75 V leading to best power conversion efficiency of 17.6%. This enhancement is attributed to the facile charge flow at the interface owing to the reduction of interfacial traps and carrier recombination with spike structure as evidenced by time-resolved photoluminescence, nanosecond transient absorption, and electrochemical impedance spectroscopy measurements.
Tin−lead (Sn−Pb)-based perovskite solar cells (PSCs) still exhibit inferior power conversion efficiency (PCE) compared to their pure Pb counterparts because of high voltage loss (V L ) and high photocurrent loss in the infrared region. This study explores that a small amount of cesium ion (Cs + ) incorporation in the lattice of Sn−Pb perovskite can reduce the relative lattice strain, which in turn decreases the V L less than 0.50 V. Moreover, surface and bulk trap densities also seem to be reduced by Cs + addition, as concluded by thermally stimulated current measurements and increased carrier lifetime by photoluminescence study. It was discovered that a small amount of Cs + lowered the Urbach energy, which can be used as a signature to optimize the optoelectronic and the photovoltaic properties of multication perovskite materials. This study further demonstrates that a high external quantum efficiency (∼80% at 900 nm) can be obtained with fluorine-doped tin oxide (FTO) glass rather than frequently used indium tin oxide (ITO) glass. The strategies employed in the work improved the open-circuit voltage to 0.81 V and gave a photocurrent density of >30 mA/cm 2 and a PCE of >20% using a band gap of 1.27 eV.
The improvement of solar cell performance
in the near-infrared
(near-IR) region is an important challenge to increase power conversion
efficiency under one-sun illumination. PbS quantum-dot (QD)-based
heterojunction solar cells with high efficiency in the near-IR region
were constructed by combining ZnO nanowire arrays with PbS QDs, which
give a first exciton absorption band centering at wavelengths longer
than 1 μm. The morphology of ZnO nanowire arrays was systematically
investigated to achieve high light-harvesting efficiency as well as
efficient carrier collection. The solar cells with the PbS QD/ZnO
nanowire structures made up of densely grown thin ZnO nanowires about
1.2 μm long yielded a maximum incident-photon-to-current conversion
efficiency (IPCE) of 58% in the near-IR region (@1020 nm) and over
80% in the visible region (shorter than 670 nm). The power conversion
efficiency obtained on the solar cell reached about 6.0% under simulated
one-sun illumination.
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