Stable, cost-effective, sustainable and recyclable perovskite photovoltaics using carbon-based electrodes

Despite the tremendously rapid development of perovskite photovoltaics (PV) in terms of power conversion efficiency (PCE) the stability of such devices typically still does not fulfill the requirements for commercialization of this technology. Up to date, PV devices with carbon-based back-electrodes have demonstrated the longest operational stability, surpassing several IEC 61215 standards, including damp-heat test, thermal cycling and maximum-power-point-tracking. Moreover, recently we reported that such modules could withstand requirements of the IEC hot-spot test (evaluating the stability of PV devices against reverse-bias degradation), which is one of the most crucial hurdles not only for perovskite PV, but even for such well-established PV technology as c-Si. Thus, devices with carbon-based electrodes represent a promising method for up-scalable manufacturing of stable and low-cost perovskite PV devices. The common assumption for evaluating the technological readiness of an emerging PV technology is to consider three key parameters: (1) power conversion efficiency, (2) cost and (3) stability. However, based on the current projections of greenhouse gas (GHG) emissions coming from PV manufacturing, the annual emissions of PV industry might become higher than national emissions of industrialized countries like France or Germany (depending on the technological learning rate). Thus, for a truly sustainable solar energy harvesting technology another aspect of (4) sustainability must be considered. We demonstrated that the production of printed carbon-based PSC have the potential to reach the lowest CO2-footprint limit possible for large scale PV applications. Beyond the production, One of the methods to reduce the GHG emissions of PV industry is the development of effective recycling strategies, where perovskite PV offers unique advantages (in comparison to for example c-Si technologies) of liquid processing. Up to now, only studies on the recyclability and life-cycle-assessments of non-encapsulated devices have been demonstrated. However, regardless of PV technology, solar modules require encapsulation to provide sufficient protection of sensitive layers constituting device stack from the ambient environment, which is especially important for perovskite modules. To demonstrate that perovskite PV devices with carbon-based electrodes can not only be stable but also recyclable, we manufactured such solar cells and modules, encapsulated with thermoplastic polyolefin and polyisobutylene edge-seal, which provides sufficient protection against moisture, passing the IEC damp-heat test. Through life-cycle assessment, we showed that most of the negative environmental impact comes from the layer deposition, rather than the environmental footprint of material itself, making the re-use of as many layers as possible the most preferable option. We demonstrate an effective mechanochemical method to remove the edge-seal and encapsulant, as well as degraded perovskite and carbon electrode, leaving metal oxide layers intact making them available for re-use. Our novel recycling method of such devices results in minimal performance loss, which helps to reduce the negative environmental impact of such devices (global warming potential in kg CO2-eq./kWp) by > 40%. Such strong reduction in the global-warming potential of perovskite solar modules with carbon-based electrodes qualifies them as truly sustainable PV technology meeting all (1-4) requirements for its introduction to the PV market.