Interfacial Connections between Organic Perovskite/n⁺ Silicon/Catalyst that Allow Integration of Solar Cell and Catalyst for Hydrogen Evolution from Water

Abstract

The rapidly increasing solar conversion efficiency (PCE) of hybrid organic–inorganic perovskite (HOIP) thin‐film semiconductors has triggered interest in their use for direct solar‐driven water splitting to produce hydrogen. However, application of these low‐cost, electronic‐structure‐tunable HOIP tandem photoabsorbers has been hindered by the instability of the photovoltaic‐catalyst‐electrolyte (PV+E) interfaces. Here, photolytic water splitting is demonstrated using an integrated configuration consisting of an HOIP/n+silicon single junction photoabsorber and a platinum (Pt) thin film catalyst. An extended electrochemical (EC) lifetime in alkaline media is achieved using titanium nitride on both sides of the Si support to eliminate formation of insulating silicon oxide, and as an effective diffusion barrier to allow high‐temperature annealing of the catalyst/TiO2‐protected‐n+silicon interface necessary to retard electrolytic corrosion. Halide composition is examined in the (FA1‐xCsx)PbI3 system with a bandgap suitable for tandem operation. A fill factor of 72.5% is achieved using a Spiro‐OMeTAD‐hole‐transport‐layer (HTL)‐based HOIP/n+Si solar cell, and a high photocurrent density of −15.9 mA cm−2 (at 0 V vs reversible hydrogen electrode) is attained for the HOIP/n+Si/Pt photocathode in 1 m NaOH under simulated 1‐sun illumination. While this thin‐film design creates stable interfaces, the intrinsic photo‐ and electro‐degradation of the HOIP photoabsorber remains the main obstacle for future HOIP/Si tandem PEC devices.

Thin film TiO2/TiN bifunctional interface enables integration of Ni5P4 electro-catalyst with GaInP2/GaAs III-V tandem photoabsorber for stable solar-driven water splitting

“…The oxygen is likely from the hydroxides on the BOE-etched GaInP2 surface prior to the TiN deposition. 25 The P L2,3-edge is identified within the GaInP2 layer (Figure 5e).…”

“…Our recent work discovered that annealing of the physical vapor deposited TiO2/TiN on n + Si at 300 °C resulted in formation of crystalline anatase phase of TiO2. 25 By contrast, the oxygen partial pressure during annealing is a critical factor that affects the crystallization of amorphous TiO2. It may be feasible to use air annealing of TiO2/TiN/GaInP2 to form a crystalline TiO2 layer for tests of further durability improvement.…”

“…Both our recent work and the literature work reveal that Ti from TiN can diffuse into Si during annealing at 300 °C. 25,37 Moreover, the profile of the Ti L2,3-edge peak changes with the depth, indicating different bonding around Ti atoms within different layers of the TiO2/TiN/GaInP2 interface. Taken together, a slight diffusion of Ti from TiN into both of these semiconductors can occur at this elevated temperature.…”

“…6 Herein, to obtain stable crystalline TiO2 and catalysts during the hightemperature annealing processes, one additional thin layer of high-density TiN as an effective diffusion barrier between TiO2 and GaInP2 is needed, which is expected to prevent the inter-diffusion during synthesis and operation. 25 TiN exhibits exceptional chemical and physical properties, including high conductivity, high density and hardness, and good corrosion resistance. 26 TiN has been used as an excellent diffusion barrier and creates stable interfaces between photoabsorbers and PGM-free catalysts such as transition metal phosphides under high-temperature synthesis conditions.…”

TiO2/TiN Interface Enables Integration of Ni5P4 Electrocatalyst with a III–V Tandem Photoabsorber for Stable Unassisted Solar-Driven Water Splitting

“…4,11,12 Other emerging thin-film photoabsorbers are being developed that face similar challenges, such as hybrid organic−inorganic perovskites, based on monolithic photoelectrodes for unassisted PEC water splitting. 13,14 One strategy to slow the photocorrosion of GaInP 2 under HER conditions is to functionalize its surface. Electronic and chemical passivation has been achieved by applying a tightly bonded layer of ultrathin AlInP and subsequently oxidizing it.…”