Low-Temperature Solution-Processed Cu₂AgBiI₆ Films for High Performance Photovoltaics and Photodetectors

Abstract

Recently, Cu2AgBiI6 semiconductor has been investigated due to the high absorption coefficient, direct bandgap, and low exciton binding energy, which are promising for eco-friendly photoelectric devices. Herein, pyridine is introduced as solvent additive to completely dissolve the solutes and form clear Cu2AgBiI6 precursor solution, which results in high-quality films and may provide a general approach for high-quality film growth of other bismuth-based metal halide semiconductors. In addition, the electronic structure of Cu2AgBiI6 has been demonstrated for the first time and shows an intrinsically weak n-type semiconductor. Furthermore, phenethylammonium iodide for surface passivation significantly improves the film quality, slightly n-dopes the material, and shifts up the band level. Finally, the photovoltaics and photodetector performance for n-i-p planar heterojunction devices have been investigated. The efficiency is up to 1%, highest for Cu2AgBiI6 solar cells and comparable with other lead-free bismuth based metal halide solar cells. Moreover, photodetectors with fast speed of rising and decaying time, especially the excellent specific photodetectivity of ∼1012 Jones within the wavelength of ∼350–600 nm, are achieved, which paves an alternative and promising strategy for the design of future commercial photodetectors that are self-powered, stable, nontoxic, etc.

Solution Processable Direct Bandgap Copper‐Silver‐Bismuth Iodide Photovoltaics: Compositional Control of Dimensionality and Optoelectronic Properties

“…The PCE and J sc achieved herein for Cu 2 AgBiI 6 compare well to those reported for Cs 2 AgBiBr 6 combined with similar ETM and HTM and are better than those provided by a range of other lead‐free perovskite‐inspired materials (Table S6, Supporting Information). [ 6a,13a,27,34 ] Furthermore, the photovoltaic metrics presented in this work are the best reported to date for the Cu x AgBiI 4+ x class of materials. As anticipated, the films produced with the solution and substrate temperatures of 100 °C produced the best results among the devices based on the Cu x AgBiI 4+ x films prepared using hot‐casting and were also better than those achieved when using antisolvent‐assisted spin‐coating (Figure S24, Supporting Information).…”

“…Moreover, no photovoltaic devices based on CuAgBiI 5 have been reported yet, while those based on Cu 2 AgBiI 6 delivered only low power conversion efficiencies below 1%. [ 27 ] Addressing this, we present herein a study of the compositional tunability of optoelectronic characteristics and associated photovoltaic performance for the Cu x AgBiI 4+ x system. One feature of the present work is the first demonstration of a solvent‐based hot‐casting method to prepare thin Cu x AgBiI 4+ x films with improved morphology and surface coverage, which allowed us to achieve the highest photovoltaic performance for these materials reported so far.…”

Enhancing the Microstructure of Perovskite‐Inspired Cu‐Ag‐Bi‐I Absorber for Efficient Indoor Photovoltaics

“…The PCE of 1.30% of the champion device is higher than the recently reported value (1%) for CABI solar cells. [ 18 ] The current density ( J )–voltage ( V ) characteristics (forward bias scans) of the champion cells are presented in Figure 3c. The devices show hysteresis between the reverse and forward voltage scans (see Figure S10a,c, Supporting Information), as reported earlier.…”

“…[ 15 ] Very recently, the PCE value of 1% was achieved through the surface passivation of CABI layer. [ 18 ] Nevertheless, the low solar PV performance can be partly attributed to CABI's bandgap of 2.06 eV, which leads to large optical losses under solar illumination. Moreover, despite the film formation optimization via a proposed two‐step annealing, [ 15,18 ] the reported CABI films presented numerous pinholes and surface cracks or small size grains of a few hundred nanometers, which may induce shunt leakage effects and are detrimental to charge transport.…”

“…[ 18 ] Nevertheless, the low solar PV performance can be partly attributed to CABI's bandgap of 2.06 eV, which leads to large optical losses under solar illumination. Moreover, despite the film formation optimization via a proposed two‐step annealing, [ 15,18 ] the reported CABI films presented numerous pinholes and surface cracks or small size grains of a few hundred nanometers, which may induce shunt leakage effects and are detrimental to charge transport. Therefore, the film growth of CABI must be optimized to achieve smoother films with continuous morphology and large‐sized grains.…”