Highly Efficient, Stable, and Scalable Integrated Hybrid Perovskite Photoelectrochemical Cells with STH>12.4% for Water Splitting

Abstract

A global effort to decrease green house emissions and the cost of renewable energy technologies such as solar and wind have triggered a systematic effort in their adoption for the generation of clean electricity. However, the widespread incorporation of photovoltaic technologies has been hindered by their costs, which are still not on-par with electricity produced using non-renewables, and by intermittency issues for solar. While batteries provide a possible solution, a key challenge is their variability and lack of long-term stability. Solar fuels, which are highly scalable and offer the stability of storage in chemical bonds are a promising solution, but the technologies that enable generation are not yet efficient, scalable, and cheap.Integrated photoelectrochemical cells (PECs) directly couple the photoabsorber to the electrolyte through anticorrosion barriers and surface-deposited electrocatalysts (Fig. 1A). State-of-the-art devices use multijunction III-V panel photoabsorbers and are limited by high cost. Alternative absorbers like Si have insufficient voltage, and particle photocatalysts, while stable, are inefficient. Halide perovskites are promising next-generation photoabsorbers, providing >2V open-circuit voltage with two devices in series (photocathode + photoanode) at low cost (estimated <$100/m2 PV panels). Yet, due to their spontaneous dissolution in water at any applied bias, PECs based on HaPs have demonstrated low efficiencies (ABPE<10%, STH<6%) and stabilities.Here, we demonstrate a high-efficiency integrated hybrid perovskite based photoelectrochemical (HaP-PEC) device, which can perform bias free water-splitting at a solar-to-hydrogen (STH) efficiency of 12.4%. The HaP-PEC is enabled by two important innovations. First, by using a novel geometry, we decouple the light-absorption and electrochemical reaction interfaces for both the photocathode and the photoanode. Second, we have developed a new corrosion barrier technology, which is modular, scalable and importantly can almost perfectly translate the photovoltaic efficiency to the catalytic site.Using this approach, we report the transformation of a p-i-n perovskite solar cell (PSC) with photoconversion efficiency (PCE) > 20% into a photocathode for HER with applied-bias photoconversion efficiency (ABPE) > 20%, almost fully translating the efficiency of the parent solar cell to the Pt catalyst (Fig. 1B). Under bias at 0V vs RHE, the device was stable for up to 8h in 0.5M H2SO4. Scale-up of the photocathode to an absorber area of ~0.43 cm2 showed a decrease in the photovoltaic PCE (~10%) but again complete preservation of the photovoltaic efficiency in the ABPE (~10%). We further demonstrate the versatility of this approach by transforming an n-i-p PSC (PCE~20%) into a photoanode for OER with ABPE ~10% (due to catalyst inefficiencies, even when using Ir) (Fig. 1B). Although the n-i-p device is incapable of extended operation in acidic media (even when biased to 1.23V vs RHE it degraded continuously over 3h), when operated in series, the tandem photocathode-photoanode system achieved bias-free water-splitting at >12.4% STH and sustained this performance for over 2h. The photoanode and the bias-free system were both limited by increased overpotential from the degradation of the OER catalyst.Broadly, we have demonstrated a photoelectrode technology which uses a low-cost photo-absorber and achieves near-equal efficiencies as the photovoltaic even at large scale. To the best of our knowledge, ours is the highest STH efficiency for an integrated solar-to-hydrogen device not containing expensive III-V photoabsorbers, and fully double that of the previous record using integrated halide perovskite photoabsorbers (~6% STH). Furthermore, our approach is reaction-agnostic due to the decoupling of light absorption and electrocatalysis. This enables a facile and low-cost pathway to arbitrary solar-powered electrochemical reactions with high solar-to-chemical efficiency. Figure 1