MACl‐Assisted Ge Doping of Pb‐Hybrid Perovskite: A Universal Route to Stabilize High Performance Perovskite Solar Cells

Abstract

Interfacial engineering, grain boundary, and surface passivation in organic–inorganic hybrid perovskite solar cells (HyPSCs) are effective in achieving high performance and enhanced durability. Organic additives and inorganic doping are generally used to chemically modify the surface contacting charge transport layers, and/or grain boundaries so as to reduce the defect density. Here, a simple but tricky one‐step method to dope organic–inorganic hybrid perovskite with Ge for the first time is reported. Unlike Ge doping to all‐inorganic perovskites, application of GeI2 in organic–inorganic perovskite precursors is challenging due to the extremely poor solubility of GeI2 in hybrid perovskite ink, leading to failure in the formation of uniform films. However, it is found that addition of methylammonium chloride (MACl) into the precursor remarkably increases the solubility of GeI2. This MACl‐assisted Ge doping of hybrid perovskites produces high‐quality crystalline film with its surface passivated with nonvolatile GeI2 (GeO2) and the volatile MACl additive also improves the uniformity of GeO2 distribution in the perovskite films. The resulting Ge‐doped mixed cation and mixed halide perovskite films with composition FA0.83MA0.17Ge0.03Pb0.97(I0.9Br0.1)3 show superior photoluminescence lifetime, power conversion efficiency above 22%, and greater stability toward illumination and humidity, outperforming photovoltaic properties of HyPSCs prepared without the Ge doping.

Lead‐Less Halide Perovskite Solar Cells

“…Lead substitutions by other elements detailed in this Review are also worth considering due to their influence mainly on perovskite film morphology and bandgap. Nevertheless, to achieve efficiencies that can be compared with Sn–Pb or pure‐Pb PSCs, the amount of substituent has to be very low (under 10%), the best efficiency reached is 22.09% but for a Ge content of only 3 mol%, [ 187 ] and yet, the stability is not good since Ge suffers from the same oxidation problem as Sn. Important work needs to be implemented to increase the amount of substituent without impacting dramatically the performances of the devices.…”

“…With this observation, in 2020, Kim et al developed a way to overcome this problem by adding methylammonium chloride (MACl) into the precursor solution with GeI 2 . [ 187 ] They found that MACl remarkably increased the solubility of GeI 2 leading to high‐quality films using a dripping method (Figure S12, Supporting Information). With GeI 2 percentage, a decreasing roughness of the perovskite film surface and grain size were found due in part to the passivation caused by the segregation of GeI 2 at GB.…”

PEAI-Based Interfacial Layer for High-Efficiency and Stable Solar Cells Based on a MACl-Mediated Grown FA0.94MA0.06PbI3 Perovskite

“…[33][34][35] Recently, MACl additive was employed to increase the solubility of GeI2 and allows the doping of the mixed cation perovskite layer with Ge. 36 Mu et al used MACl combined with FAI in stoichiometric amounts to obatined mixed Cl and I halide perovskite compounds. 30 Kim et al were the first to employ MACl as an additive in the perovskite T. Zhu, D. Zheng, J. Liu, L. Coolen, Th.…”

Intermediate‐Adduct‐Assisted Growth of Stable CsPbI2Br Inorganic Perovskite Films for High‐Efficiency Semitransparent Solar Cells

“…Among light‐absorbers for solar cells, perovskite stands out due to its direct and tunable bandgap to absorb enough photons, [ 15–19 ] and the PCE of perovskite solar cell (PSC) has increased from 3.8% to 25.2%. [ 20–24 ] At present, methylammonium lead iodine (MAPbI 3 ) with a bandgap of 1.6 eV is widely applied in ST‐PSC, [ 25–27 ] however, its thickness must be greatly reduced for achieving enough AVT (>20%) and the J sc is also reduced accordingly. [ 28 ] In addition, it is difficult for MAPbI 3 to obtain a high V oc exceeding 1.2 V. Consequently, most reported PCEs of ST‐PSCs are below 12% when the AVT is higher than 20%.…”