Stoichiometric Engineering of Cs₂AgBiBr₆ for Photomultiplication-Type Photodetectors

Abstract

Photomultiplication (PM)-type photodetectors with a high external quantum efficiency (EQE) can be realized through adequately engineered trap states and trap-assisted charge injection. By strategically introducing slightly rich Bi and highly rich Br stoichiometric conditions, efficient trap states are realized for holes in lead-free Cs1.98AgBi1.15Br7.9 double perovskite (DP). With the diode structure of ITO/SnO2/Cs1.98AgBi1.15Br7.9/poly­(3-hexylthiophene) (P3HT)/MoO x /Ag, where SnO2 and P3HT layers are used as the hole- and electron-blocking layers, respectively, successful realization of the selective hole trap and the resulting band bending/electron injection at the anode interface is demonstrated. As a result, a high EQE of ∼16,000%, responsivity of ∼50 A W–1, and specific detectivity of over 1012 Jones at −3 V are demonstrated. The origin of the suggested PM mechanism is discussed using photophysical and optoelectronic measurements and theoretical studies. This work ensures the successful demonstration of PM-type photodetectors using lead-free Cs2AgBiBr6 DP through strategic trap engineering.

Short-Wave Infrared Emissions from Te4+–Ln3+ (Ln: Er, Yb)-Codoped Cs2NaInCl6 Double Perovskites

“…Similar strategies of Sb 3+ –Ln 3+ and Bi 3+ –Ln 3+ codoping in metal halide double perovskites have been reported earlier. − The Sb 3+ and Bi 3+ ions have two electrons in the outer most s-orbital ( n s 2 ), and can absorb UV lights owing to n s 2 → n s 1 n p 1 transitions. − As shown in Figure , Sb 3+ and Bi 3+ doping in Cs 2 NaInCl 6 introduces new absorption peaks at 263 (weak absorption at 335 nm as well) and 327 nm, respectively, below the band gap of the host. − This sub-band-gap level absorptions reduces the input excitation energy of Sb 3+ - and Bi 3+ -doped Cs 2 NaInCl 6 by 1.4 and 1.3 eV, respectively, compared to the host band gap. Also, the host does not get excited in the optical excitation process, increasing its photostability.…”

Stoichiometric Engineering of Ag2S Nanocrystals to Realize High Performance for Organic–Inorganic Hybrid Photodiodes

“…The structures of hole- and electron-only devices are ITO/PEDOT/PSS/active layer/MoO x /Ag and Al/active layer/Al, respectively. In the ideal diode operation condition, the SCLC current of J SCLC through an active layer with thickness of L increases approximately with the square of the applied voltage of V , that is, follows the equation of the SCLC , J normalS normalC normalL normalC = 9 ε 0 ε r μ V 2 8 L 3 where ε 0 is the vacuum permittivity, ε r is the relative dielectric permittivity, and μ is the SCLC mobility. The calculated SCLC hole and electron mobilities of the P3HT matrix with and without Ag 2 S NCs are shown in Figure c,d.…”

“…As the trap is filled in the trap-filling (TFL) region, the current shows a steep increase with m above 2. The voltage at which all the traps are filled was determined by the trap density , V normalT normalF normalL = q n normalt normalr normala normalp L 2 2 ε 0 ε r where q is the elementary charge. The calculated mobility and trap density for each device are summarized in Table S3.…”

“…Consequently, Si-based CMOS technology requires not only a thick active layer (>3 μm) for the photodiode but also additional light shield layers between adjacent red, green, and blue (R/G/B) pixels. These challenges present major obstacles in highly integrated image sensors for novel technology. − …”

High-Performance Negative Self-Powered α-MoO3/Ir/α-MoO3 Photodetectors: Probing the Influence of Coulomb Deep Traps

“…Nonetheless, the functioning of the MoO 3 device is impacted by elevated levels of bulk defects, − leading to instabilities in the flat-band voltage. The presence of these defects becomes evident through several experimental methods, such as trap-assisted electron conduction involving the Poole–Frenkel mechanism, − direct electron injection, and optical absorption . Although the specific energy levels of the defects vary across different experiments, the oxygen vacancy is typically identified as their shared physical source. − By this means, an oxygen vacancy has become interesting with direct contributions to optoelectronic conductivity .…”