Efficient and stable formamidinium–caesium perovskite solar cells and modules from lead acetate-based precursors

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Abstract

For the first time, formamidinium–caesium perovskite thin films were successfully synthesised from a lead acetate-based precursor. Efficient perovskite solar cells (21.0%) and modules (18.8%) have been produced using blade coating techniques.

Abstract

Controlling the crystallization process of perovskite thin films to obtain a high-quality material is one of the most challenging aspects for upscaling perovskite solar cell (PSC) technology. The use of non-halide lead sources, such as lead acetate, is a potential solution to this issue due to the fast perovskite crystallization process triggered by the facile removal of acetate during post-annealing. However, to date, lead acetate has been used exclusively as a precursor for the synthesis of methylammonium (MA) or caesium (Cs) based perovskites, which are unstable and less efficient. Here, we expand the lead acetate precursor route to form mixed A-cation perovskites, namely, formamidinium–caesium lead perovskite. High-quality large-area formamidinium–caesium mixed-cation perovskite films were produced by blade-coating a lead acetate-based precursor formulation in an ambient laboratory environment, with the use of NH ₄ ⁺ as a volatile cation to drive off acetate during annealing, leading to formation of PSCs with a power conversion efficiency (PCE) of up to 21.0%. Blade coated mini-modules with an aperture area of 10 cm ² displayed PCEs of up to 18.8%. The encapsulated PSCs showed excellent thermal stability, with no evidence of efficiency loss after 3300 hours at 65 °C.

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Electron-hole diffusion lengths exceeding 1 micrometer in an organometal trihalide perovskite absorber.

Samuel D Stranks, Marcelo J P Alcocer, Christopher Menelaou … (2015)

Organic-inorganic perovskites have shown promise as high-performance absorbers in solar cells, first as a coating on a mesoporous metal oxide scaffold and more recently as a solid layer in planar heterojunction architectures. Here, we report transient absorption and photoluminescence-quenching measurements to determine the electron-hole diffusion lengths, diffusion constants, and lifetimes in mixed halide (CH3NH3PbI(3-x)Cl(x)) and triiodide (CH3NH3PbI3) perovskite absorbers. We found that the diffusion lengths are greater than 1 micrometer in the mixed halide perovskite, which is an order of magnitude greater than the absorption depth. In contrast, the triiodide absorber has electron-hole diffusion lengths of ~100 nanometers. These results justify the high efficiency of planar heterojunction perovskite solar cells and identify a critical parameter to optimize for future perovskite absorber development.

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Efficient hybrid solar cells based on meso-superstructured organometal halide perovskites.

Michael Lee, Joël Teuscher, Tsutomu Miyasaka … (2012)

The energy costs associated with separating tightly bound excitons (photoinduced electron-hole pairs) and extracting free charges from highly disordered low-mobility networks represent fundamental losses for many low-cost photovoltaic technologies. We report a low-cost, solution-processable solar cell, based on a highly crystalline perovskite absorber with intense visible to near-infrared absorptivity, that has a power conversion efficiency of 10.9% in a single-junction device under simulated full sunlight. This "meso-superstructured solar cell" exhibits exceptionally few fundamental energy losses; it can generate open-circuit photovoltages of more than 1.1 volts, despite the relatively narrow absorber band gap of 1.55 electron volts. The functionality arises from the use of mesoporous alumina as an inert scaffold that structures the absorber and forces electrons to reside in and be transported through the perovskite.