p-type Cu 2 O thin films doped with trivalent cation boron are demonstrated for the first time as an efficient hole-selective layer for c-Si heterojunction solar cells. Cu 2 O and Cu 2 O:B films were deposited by rf magnetron sputtering, and the optical and electrical properties of the doped and undoped films were investigated. Boron doping enhanced the carrier concentration and the electrical conductivity of the Cu 2 O film. The band alignment of the Cu 2 O:B/ Si heterojunction was investigated using XPS and UPS measurements. The Cu 2 O:B/Si interface has a valance band offset of 0.08 eV, which facilitates hole transport, and a conduction band offset of 1.35 eV, which blocks the electrons. A thin SiO x tunnel oxide interlayer was also explored as the passivation layer. The initial trials of incorporating this Cu 2 O:B layer as a hole transporting layer in a single heterojunction solar cell with the structure, ITO/Cu 2 O:B/n-Si/Ag, and a cell area of 1 cm 2 yielded an open-circuit voltage of 370 mV, a short-circuit current density of 36.5 mA/cm 2 , and an efficiency of 5.4%. This p-type material could find potential applications in various optoelectronic applications like organic solar cells, TFTs, and LEDs.
Inorganic materials, such as MoOx and V2Ox, are increasingly explored as hole transport layers for perovskite based solar cells. Due to their large work function and n-type nature, hole collection mechanisms with such materials are fundamentally different, and the associated device optimizations are not well elucidated. In addition, prospects of such architectures against the challenges posed by ion migration are yet to be explored—which we critically examine in this contribution through detailed numerical simulations. We find that, for similar ion densities and interface recombination velocities, ion migration is more detrimental for perovskite solar cells with n-type hole transport layers with much lower achievable efficiency limits (∼21%). The insights shared by this work could be of broad interest to critically evaluate the promises and prospects of n-type materials as hole transport layers for perovskite solar cells.
The presence of mobile ions in perovskites is well known to influence the device electrostatics leading to a wide variety of anomalous characteristics related to hysteresis, efficiency degradation, low frequency capacitance, large signal switching, etc. Accordingly, the ion mobility is understood to a have a critical influence on the associated time constants/delays. Quite contrary to this broadly accepted thought, here we suggest that the time delays associated with large signal switching could show a universal behavior dictated by electronic dipoles, rather than ionic dipoles. Due to the resultant sudden and dramatic collapse of a contact layer depletion region, large signal switching delays are independent of ion mobilities. Furthermore, our detailed numerical simulations, supported by experimental results, indicate that terminal currents show a near steady state behavior well ahead of the relaxation of ionic distributions. These results have interesting implications toward the understanding and optimization of perovskite based electronic devices, including solar cells, LEDs, resistive memories, and ferroelectric memories.
Simultaneous requirement of excellent interface passivation and low thermal budget is a desirable feature for low cost Si based carrier selective solar cells. Accordingly, Titanium dioxide (TiO2), a widely used electron selective material, finds challenges related to thermal annealing like phase change and compatibility with thermal budget of hole transport layers. To address this, here we report a H2 plasma treatment process at room temperature which significantly reduces the surface recombination velocity (∼40 cm/s). Consequently, the reverse saturation current of the Si-TiO2 diode improves by a factor of 40, built-in potential improves by 100 mV, and the diode exhibits a near unity ideality factor. Using the same method, our Si-based double heterojunction solar cell results in an absolute increase of 2.4% in efficiency over devices with conventional thermal annealing. Given the ease of implementation and excellent performance, the proposed method is a promising alternative to thermal annealing for Si based heterojunction devices.
Successful
commercialization of Perovskite/Si tandem solar cells
(P/Si TSCs) needs a priori estimation of technological benchmarks
to outperform c-Si based technologies under field conditions. To this
end, through detailed numerical simulations and analytical modeling,
we unravel a unique scaling law for the evolution of the efficiency
and temperature coefficient of P/Si TSCs. Accordingly, we estimate
annual energy yields of P/Si tandem solar cells, which account for
the daily and seasonal variations in solar spectrum and ambient conditions.
Through this, we identify the limits of ion migration and lifetime
degradation until which P/Si TSCs remain competitive. These results
could be of broad relevance for material/interface engineering approaches
and physics-based accelerated tests to ensure long-term stability
and module reliability.
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