Development of Stable and Efficient Tin Perovskite Solar Cells Using Anilinium Hypophosphite Additive, and Perylene-diimide as a Copper Interfacial Layer

Abstract

Tin perovskite solar cells (Sn-PSCs) have attracted a tremendous attention due to the robust optoelectronic properties of Sn-perovskite materials. The band gap of Sn-perovskite (~1.3-1.5 𝑒𝑉), is within the optimal band gap for fabrication of high performing single junction solar cells. However, the power conversion efficiency (PCE) and stability of Sn-PSCs are still low despite the good Sn-perovskite optoelectronic properties. The primary challenge is the ease of oxidation of Sn2+ ions in the Sn-perovskite absorber material, and uncontrollable crystallization during Snperovskite film formation. In the first part of this study, tin fluoride (SnF2) and anilinium hypophosphite (AHP) were used to inhibit the oxidation of Sn2+ and to maintain the stability of Sn- PSCs. The crystallization was controlled by using solvent engineering technique by mixing N, Ndimethylformamide (DMF), and dimethyl sulfoxide (DMSO), and using chlorobenzene (CB) as an antisolvent. Combining SnF2 and AHP resulted in stable films with superior optoelectronic properties. The primary reason was the ability of AHP to interact with SnF2 to produce a complex double salt (Sn(H2PO2)2.SnF2) which passivated the grain boundaries and surface of the absorber films. The passivated films were prevented from direct contact with oxygen and moisture, which are the main degrading agents, thereby making the films more stable. SnF2 and AHP mixture was used to fabricate two Sn-PSCs with absorber layers of FA0.50MA0.45PEA0.05SnI3.00 and FASnI3. The PCE of Sn-PSCs from FA0.50MA0.45PEA0.05SnI3.00 absorber layer was up to 6.87% with a stability of 97% after 720 hours of storage in a nitrogen environment. The efficiency of Sn-PSCs from FASnI3 absorber material rose to 5.48% from 4.04% of the control device. In the second part of this study, perylene-diimide (PDINN) was utilized as a cathode interfacial layer to enhance the performance of Sn-PSCs. Copper (Cu) was used instead of the commonly used silver (Ag) because of its ability to resist corrosion from halide materials originating from the perovskite due to iodine ion migration and diffusion. PDINN was used as a cathode interfacial layer instead of the usual bathocuproine (BCP) because of its better electrical and physical properties. The Sn-PSCs based on PDINN achieved an efficiency of up to 10.99% with an improved stability. The PDINN-based Sn-PSC maintained up to 80% of its PCE even after exposure to the atmospheric air of relative humidity ~35 - 45% and temperature ~19 - 25℃. The stability and magnified PCE of PDINN based Sn-PSCS was due to its hydrophobic nature making it difficult for moisture penetration, and its ability to efficiently-transport photogenerated charges at the electron transport layer (ETL)/cathode interface.