Electrochemically Assisted Growth of CsPbBr₃‐Based Solar Cells Without Selective Contacts

Abstract

In this work we report a simple and cost-effective CsPbBr 3based solar cell without ordinary selective contacts. To do so we follow an electrochemical approach consisting of three successive steps: (1) electrodeposition of PbO 2 directly on top of FTO substrates, (2) heterogeneous phase reaction with gaseous HBr and (3) spin-coating of methanolic CsBr solutions followed by annealing. This method is more adequate for largescale environmentally friendly production as it reduces chemical waste, particularly toxic lead. The resulting films were structurally and optically characterized showing good coverage of the FTO substrates, absence of defects such as pinholes and orthorhombic structure. Photovoltaic and impedance characterization was carried out by pressing a carbon coated metal spring onto the CsPbBr 3 film until obtaining maximized opencircuit potential (V oc) and short-circuit photocurrent density (j sc) under simulated sunlight. The stabilized current at fixed voltage (SCFV) technique gave a maximum PCE value of 2.70 % close to devices with similar configuration. Impedance measurements demonstrated analogous behavior to that of state-of-art CsPbBr 3 based solar cells, comprising a recombination arc at mid-high frequencies, geometrical capacitance and ideality factors closed to 2, typical of SRH recombination in the perovskite bulk.

Photophysical and Photoelectrochemical Properties of CsPbBr3 Films Grown by Electrochemically Assisted Deposition

“…This value is in the same order of that calculated from the solar simulator (AM 1.5 spectrum) used in the photoelectrochemical measurements (4.5×10 16 photons s −1 cm −2 ). Here, only photons with sufficient energy to create mobile electron‐hole pairs were considered, that is those with energy higher than that corresponding to the previously determined bandgap (511 nm) [33] . On the other hand, very recently Herz and colleagues have proven the short lifetimes of photogenerated carriers (∼ns) and the prevalence of monomolecular recombination for polycrystalline CsPbBr 3 films grown on quartz at illumination fluences several orders of magnitude higher than those calculated in our experiments [99] .…”

“…Recombination studies also revealed the prevalence of Schockley-Read-Hall mechanism in this FTO/MAPI interphase as in the case of our recently reported FTO/CsPbBr 3 /C solar cell. [33,100] Regarding the aforementioned analysis, if it is assumed that CsPbBr 3 films grown either on quartz or FTO have similar short carrier lifetimes at room temperature, this feature would not contribute to compensate the usual poor charge collection in FTO/perovskite interphases. [100,102] In fact, carrier lifetimes in the order of microseconds would be necessary to suppress recombination in such interphase thus improving charge collection in FTO.…”

“…An interesting perspective is also given by G. Hodes who compared the mass consumption of lead per power unit from a car and a perovskite solar cell thus demonstrating a transition to a less lead‐based energy generation similarly to the diminishing of carbon footprint [43] . Taking into account this issue, recently, our group has reported a new method to produce selective contact free CsPbBr 3 based solar cells, using an electrochemically assisted method that is both simple, lead waste saving and potentially scalable to fix lead on electrodes compared with other techniques such as spin‐coating [33] . Besides, it was also shown that the power conversion efficiencies of the obtained samples are close to the state‐of‐the‐art values, even without the need of using neither electron nor hole transporting layers.…”

Electrodeposition as a Versatile Preparative Tool for Perovskite Photovoltaics: Aspects of Metallization and Selective Contacts/Active Layer Formation

“…Unlike the ED of TMOs, one of the perovskites presents the (important) difference that the different steps are conducted in different processes and environments and not at the same time. For the electrochemical preparation of perovskites, two different pathways can be outlined (Figure 4): it is possible to deposit lead oxide PbO 2 (Figure 4a) [68,69] or PbO [70] similarly to what discussed in the case of transition metal oxides. The PbO 2 film requires a Pb 4þ reduction step, which can be carried out with H 2 [71] or halohydric acids.…”

“…The PbO 2 film requires a Pb 4þ reduction step, which can be carried out with H 2 [71] or halohydric acids. [68,72] The PbO film is converted to PbI 2 by acid leaching in hydroiodic acid (HI) solution and then submerged to a methylammonium iodide (MAI) solution to obtain the perovskite in the final state of utilization. Alternatively, the conversion steps from lead oxides to lead halide perovskites can be conducted in the gas phase, [72] as demonstrated on textured Si.…”