Question

1. perovskite solar cells convert light into electricity more efficiently than earlier kinds of solar cells, and manufacturing advances have recently made them commercially attractive. one limitation of the cells, however, has to do with their electron transport layer (etl), through which absorbed electrons must pass. often the etl is applied through a process called spin coating, but such etls are fairly inefficient at converting input power to output power. andré taylor and colleagues tested a novel spray coating method for applying the etl. the team produced etls of various thicknesses and concluded that spray coating holds promise for improving the power conversion efficiency of etls in perovskite solar cells.

which choice best describes data from the graph that support taylor and colleagues’ conclusion?
a) both the etl applied through spin coating and the etl applied through spray coating showed a power conversion efficiency greater than 10% at their lowest performing thickness.
b) the lowest performing etl applied through spray coating had a higher power conversion efficiency than the highest performing etl applied through spin coating.
c) the highest performing etl applied through spray coating showed a power conversion efficiency of approximately 13%, while the highest performing etl applied through spin coating showed a power conversion efficiency of approximately 11%.
d) there was a substantial difference in power conversion efficiency between the lowest and highest performing etls applied through spray coating.

Explanation:

To determine the correct option, we analyze each choice based on the conclusion that spray - coated ETLs hold promise for improving power conversion efficiency (implying spray - coated ETLs have better efficiency than spin - coated ones in relevant cases):

• Option A: Just stating that both have efficiency > 10% at their lowest - performing thickness does not show that spray - coated is better. It does not support the conclusion about spray - coated ETLs being better for efficiency improvement.
• Option B: The "lowest - performing ETL through spray coating" and "highest - performing ETL through spin coating" are not the right comparison groups. We should compare the performance of spray - coated and spin - coated ETLs in a more relevant way (like their highest or typical performances) to show the advantage of spray coating.
• Option C: If the highest - performing ETL with spray coating has ~13% efficiency and the highest - performing with spin coating has ~11%, this shows that spray - coated ETLs can achieve a higher power conversion efficiency at their best, which supports the idea that spray coating holds promise for improving efficiency.
• Option D: A substantial difference within spray - coated ETLs (between their lowest and highest) does not tell us anything about how spray - coated compares to spin - coated. It does not support the conclusion about spray coating being better than spin coating for efficiency improvement.

Answer:

C) The highest performing ETL applied through spray coating showed a power conversion efficiency of approximately 13%, while the highest performing ETL applied through spin coating showed a power conversion efficiency of approximately 11%.