Scalable Processing of Low-Temperature TiO₂ Nanoparticles for High-Efficiency Perovskite Solar Cells

Abstract

Most high-efficiency perovskite solar cells (PSCs) rely on titanium dioxide (TiO2) electron transport layers (ETLs) that are usually processed at high temperature (>450 °C). Consequently, a fully solution-based process of PSCs with TiO2 ETL on inexpensive flexible polymer substrates is not feasible. Therefore, a scalable low-temperature TiO2 ETL is developed based on presynthesized crystalline nanoparticle TiO2 (np-TiO2). The presented synthesis process offers control over the doping, the hydrodynamic diameter, and the solvent of the np-TiO2. High initial power conversion efficiency (PCE) of 19.5% (stabilized at 18.2%) of PSC processed on the np-TiO2 ETL is demonstrated with spin-coated methylammonium lead iodide (CH3NH3PbI3). Furthermore, it is shown that other perovskite absorber layers that include evaporated CH3NH3PbI3 and triple cation perovskite, Cs0.1(MA0.17FA0.83)0.9Pb­(I0.83Br0.17)3, also show very high initial PCE, 14.5% and 19%, respectively. The possibility of doping the np-TiO2 with niobium (Nb5+) also reduces the resistance of the np-TiO2 ETL, allowing for thick ETLs that are beneficial for rough substrates. Facile upscaling of the deposition of the np-TiO2 ETL by inkjet printing, blade coating, and slot-die coating is also demonstrated, having high uniformity, resulting in prototype PSCs with a stable PCE > 15%.

Challenges and approaches towards upscaling the assembly of hybrid perovskite solar cells

“…5c. 76 Scalable fabrication of PSCs depending on TiO 2 nanoparticles deposited by inkjet-printing as well as slot-die methods exhibits high PCE (measured in backward and forward directions) compared to the samples attained by the spin coating technique as shown in Fig. 5d and f. Likewise, PCE at a persistent voltage up to the maximum power point (MPP) was checked for both devices ( Fig.…”

Laminated Perovskite Photovoltaics: Enabling Novel Layer Combinations and Device Architectures

“…The triple‐cation perovskite absorber solution Cs 0.1 (MA 0.17 FA 0.83 ) 0.9 Pb(I 0.83 Br 0.17 ) 3 was prepared according to ref. with the precursors of methylammonium bromide (MABr, GreatCell Solar), formamidinium iodide (FAI, GreatCell Solar), lead iodide (PbI 2 , TCI), lead bromide (PbBr 2 , TCI), and cesium iodide (CsI, Alfa Aesar). Two solutions were prepared: 1) CsI in dimethyl sulfoxide (DMSO; 1.5 m , Sigma Aldrich) and 2) FAI (1 m ), PbI 2 (1.1 m ), MABr (0.2 m ), and PbBr 2 (0.22 m ) in dimethylformamide:DMSO 4:1 v:v. An 88.9 µL aliquot of solution 1 was transferred into solution 2 and then spin‐coated by two following steps: 1) 1000 rpm (acceleration rate 5000 rpm s −1 ) for 10 s, 2) 6000 rpm (acceleration rate 5000 rpm s −1 ) for 20 s. 6–7 s before the end of second step 100 µL chlorobenzene (Sigma Aldrich), as anti‐solvent, was released on the spinning substrate.…”

“…In this regard, the HTLs, copper iodide (CuI), copper thiocyanate (CuSNC), and nickel oxide (NiO x ) have been shown to promise good intrinsic chemical stability compared to the commonly used organic HTL spiro‐OMeTAD . In addition, ETLs like zinc oxide (ZnO), tin oxide (SnO 2 ), and mesoporous titanium dioxide (TiO 2 ) are known to be intrinsically stable and have been demonstrated to result in highly efficient and stable perovskite solar cells …”

Room‐Temperature‐Processed Fullerene/TiO2 Nanocomposite Electron Transporting Layer for High‐Efficiency Rigid and Flexible Planar Perovskite Solar Cells

“…[ 16–21 ] The highest efficiency, >18%, was recently achieved for a flexible PSC. [ 22–25 ] A low‐temperature‐processed TiO 2 ETL mainly comprises TiO 2 NPs; therefore, surfactants or other insulating materials are required to avoid aggregation and enhance the interconnection of TiO 2 NPs. [ 14,22,25 ] This leads to low‐electrical‐conductivity Lt‐TiO 2 films that cause charge accumulation and carrier recombination in bulk ETL or the PSK/ETL interface, with the corresponding solar cell exhibiting high current hysteresis and poor long‐term stability.…”

“…[ 22–25 ] A low‐temperature‐processed TiO 2 ETL mainly comprises TiO 2 NPs; therefore, surfactants or other insulating materials are required to avoid aggregation and enhance the interconnection of TiO 2 NPs. [ 14,22,25 ] This leads to low‐electrical‐conductivity Lt‐TiO 2 films that cause charge accumulation and carrier recombination in bulk ETL or the PSK/ETL interface, with the corresponding solar cell exhibiting high current hysteresis and poor long‐term stability. [ 11,26 ] Recently, a simple ball milling method was reported to prepare an anatase TiO 2 NPs (G‐TiO 2 NPs) suspension in isopropanol at room temperature (RT, ≈30 °C) from bulk TiO 2 powder without adding a surfactant.…”