Abstract
Lead (Pb)–Tin (Sn) mixed perovskites suffer from large open-circuit voltage (Voc) loss due to the rapid crystallization of perovskite films, creating Sn and Pb vacancies. Such vacancies act as defect sites expediting charge carrier recombination, thus hampering the charge carrier dynamics and optoelectronic properties of the perovskite film. Here, we report the passivation of these defects using a controlled amount of 2-phenylethylazanium iodide (PEAI) in perovskite precursor solution as a dopant to enhance the performance of the 1.25 eV Pb–Sn low-bandgap perovskite solar cell. It was found that the incorporation of PEAI in the perovskite precursor not only improves the perovskite film quality and crystallinity but also lowers the electronic disorder, thereby enhancing the open-circuit voltage up to 0.85 V, corresponding to Voc loss as low as 0.4 V and the power conversion efficiency up to 17.33%. The value of Voc loss obtained with this strategy is among the least obtained for similar band gap Pb–Sn low-bandgap perovskite solar cells. Furthermore, the ambient and dark self-stability of the PEAI-treated devices were also enhanced. This work presents a simple doping strategy to mitigate the Voc loss of Pb–Sn mixed low-bandgap perovskite solar cells.
Highlights
Benefiting from the advantages such as long wavelength absorption and less thermalization loss, perovskite−perovskite multi-junction solar cells have been pursued to overcome the efficiency limit of the single-junction perovskite solar cells.[14−17] Hybrid Pb−Sn perovskites have gained much attention to be applied as low-bandgap perovskites for allperovskite tandem solar cells because of their tunable band gaps (1.2−1.5 eV) and extended range of photon absorption.[7,18]
Much focus has been on surface, interface, solvent, and additive engineering to improve both the film quality and overall device performance of the Pb−Sn mixed low-bandgap solar cell.[7,14,17,19−32] In particular, Yan group adopted several strategies such as thickness optimization and incorporation of bromine and guanidinium thiocyanate in the perovskite precursor which has led to a power conversion efficiency (PCE) of over 20%.7,25,33−35 Xu and co-workers used the ultrathin bulk-heterojunction organic semiconductor (PBDB-T:ITIC) layer as an intermediary between the hole-transporting layer and the Pb-Sn-based perovskite layer to minimize the photovoltage loss in a 1.25 eV
We studied the additive effect of 2-phenylethylazanium iodide (PEAI) salt to the Pb−Sn mixed low-bandgap perovskite precursor solution and found that the addition of a trace amount of PEAI into the perovskite precursor modulates the perovskite formation process and improves crystallinity, passivates the surface defects, reduces electronic disorder, and improves the overall perovskite film quality
Summary
Organic−inorganic metal halide perovskite solar cells have witnessed significant progress in the last decade with a singlejunction cell-level certified power conversion efficiency (PCE) of 25.2%, already surpassing the widely deployed multicrystalline silicon and thin-film technologies.[1−7] Extensive research on device architecture, chemical composition, and efficient fabrication protocol, including engineering of interfaces, band gap, solvents, and additives, have been the backbone of this success.[8−11]. The open-circuit voltage (Voc) of the device is seriously compromised This demands a proper passivation strategy that can effectively improve the surface quality of the perovskite film and mitigate the photovoltage loss combating the non-radiative recombination in hybrid Pb−Sn perovskite solar cells. Much focus has been on surface, interface, solvent, and additive engineering to improve both the film quality and overall device performance of the Pb−Sn mixed low-bandgap solar cell.[7,14,17,19−32] In particular, Yan group adopted several strategies such as thickness optimization and incorporation of bromine and guanidinium thiocyanate in the perovskite precursor which has led to a PCE of over 20%.7,25,33−35 Xu and co-workers used the ultrathin bulk-heterojunction organic semiconductor (PBDB-T:ITIC) layer as an intermediary between the hole-transporting layer and the Pb-Sn-based perovskite layer to minimize the photovoltage loss in a 1.25 eV low-bandgap perovskite solar cell and obtained a remarkably high Voc up to 0.86 V.36.
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