Monovalent Cation Doping of CH₃NH₃PbI₃ for Efficient Perovskite Solar Cells

Abstract

Here, we demonstrate the incorporation of monovalent cation additives into CH3NH3PbI3 perovskite in order to adjust the optical, excitonic, and electrical properties. The possibility of doping was investigated by adding monovalent cation halides with similar ionic radii to Pb2+, including Cu+, Na+, and Ag+. A shift in the Fermi level and a remarkable decrease of sub-bandgap optical absorption, along with a lower energetic disorder in the perovskite, was achieved. An order-of-magnitude enhancement in the bulk hole mobility and a significant reduction of transport activation energy within an additive-based perovskite device was attained. The confluence of the aforementioned improved properties in the presence of these cations led to an enhancement in the photovoltaic parameters of the perovskite solar cell. An increase of 70 mV in open circuit voltage for AgI and a 2 mA/cm2 improvement in photocurrent density for NaI- and CuBr-based solar cells were achieved compared to the pristine device. Our work paves the way for further improvements in the optoelectronic quality of CH3NH3PbI3 perovskite and subsequent devices. It highlights a new avenue for investigations on the role of dopant impurities in crystallization and controls the electronic defect density in perovskite structures.

Perovskite Solar Cells: From the Atomic Level to Film Quality and Device Performance

“…The approach of mixing various cations may be extended even further. At the smaller end, Na and K could be suitable cation candidates . However, as the ionic radii decrease, it seems less likely that a modification of the perovskite lattice is feasible.…”

Review of Novel Passivation Techniques for Efficient and Stable Perovskite Solar Cells

“…Defect passivation that eliminates charge accumulation at the ETL/perovskite interface can alleviate hysteresis caused by interface defects and ETL trap states . A common approach for ETL defect passivation includes the use of chlorine such as TiCl 4 chemical bath deposition (CBD) or Cl‐doping of ETL . Tan et al developed a contact‐passivation method that uses a chlorine‐capped TiO 2 colloidal nanocrystal film to mitigate interfacial recombination and to improve interface binding in planar structured perovskite solar cells.…”

Charge extraction via graded doping of hole transport layers gives highly luminescent and stable metal halide perovskite devices

“…Sources of instability in PSCs originate not only from their individual layers [e.g., perovskite layer ( 17 ) and charge-transporting layers ( 18 )] but also from their interfacial regions ( 19 ). The stability of PSCs has improved significantly through changes in the perovskite composition ( 20 ) [e.g., doping with monovalent cations ( 12 , 21 , 22 )] and substitution of organic HTLs for inorganic counterparts ( 23 , 24 ). However, the overall device stability is still far from the industrial standard where the most prominent source of instabilities arises from the HTL electrode (e.g., Spiro-OMeTAD), for example, the migration of dopants ( 25 ) (e.g., Li) and metal from the PSC electrode, particularly at elevated temperatures ( 26 ).…”