Improvements to perovskite solar cells (PSCs) have focused on increasing their power conversion efficiency (PCE) and operational stability and maintaining high performance upon scale-up to module sizes. We report that replacing the commonly used mesoporous–titanium dioxide electron transport layer (ETL) with a thin layer of polyacrylic acid–stabilized tin(IV) oxide quantum dots (paa-QD-SnO ₂ ) on the compact–titanium dioxide enhanced light capture and largely suppressed nonradiative recombination at the ETL–perovskite interface. The use of paa-QD-SnO ₂ as electron-selective contact enabled PSCs (0.08 square centimeters) with a PCE of 25.7% (certified 25.4%) and high operational stability and facilitated the scale-up of the PSCs to larger areas. PCEs of 23.3, 21.7, and 20.6% were achieved for PSCs with active areas of 1, 20, and 64 square centimeters, respectively.

Transient photoconductivity measurements carried out on bulk heterojunction (BHJ) solar cells demonstrate the competition between carrier sweep-out by the internal field and the loss of photogenerated carriers by recombination. The transient photoconductance data imply the existence of a well-defined internal field; carrier sweep-out is proportional to the magnitude of the internal field and limited by the carrier mobility. At external voltages near open circuit where the internal field approaches zero, the photocurrent decays because of the recombination of photogenerated mobile carriers. Mobility and recombination lifetimes are evaluated for carriers in poly[3-hexylthiophene] (P3HT): [6,6]-phenyl-C61-butyric acid methyl ester (PC60BM) and poly[N-9$'${}$'${}-hepta-decanyl-2,7-carbazole-alt-5,5-(4$'${},7$'${}-di-2-thienyl-2$'${},1$'${},3$'${}-benzothiadiazole)] (PCDTBT): [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) solar cells.