Enhancing the viability of p-i-n perovskite solar cells with printable carbon cathode: Origin of polarity inversion

Perovskite solar cell is an emerging photovoltaic technology that is potentially easy to manufacture at large scale. However, bringing these devices from the lab to industrial production may require every layer, especially the rear electrode, to be fabricated using low cost, high throughput printing methods. To date, most high efficiency devices rely on expensive metal electrodes such as silver, which increases costs and reduces the device s long term stability. Carbon is an abundant, printable, and chemically stable alternative and has been successfully used in one common device layout, the n i p so called conventional perovskite architecture. Yet, in the p i n so called inverted architecture, carbon has fundamentally been incompatible because it collects the wrong type of electrical charge. This work resolves this long standing incompatibility. We demonstrate that carbon can be used as the electron collecting electrode in inverted perovskite solar cells by introducing a tailored ultra thin tin oxide interlayer. This interlayer is both mechanically strong to survive printing and electronically tuned to overcome the inherent energy barrier that previously prevented electrons from flowing into carbon. By understanding and controlling how atomic level defects in tin oxide influence charge transfer, we convert carbon from a hole collecting material into an efficient electron collector. The result is a carbon based device with comparable performance, remarkably longer operational lifetime, and over 60 lower material cost, compared with its silver based counterparts. Our findings establish a general physical principle for designing interfaces between n type metal oxides and carbon for electron extraction, opening a new pathway toward metal free, scalable, and durable perovskite solar cells. In doing so, we address one of the last major obstacles to fully printed, low cost solar manufacturing at industrial scale