While employing charge transport layers (CTLs) in optoelectronic devices including hybrid perovskite solar cells is essential for high performance, using solution-processed organic semiconductor-based CTLs poses challenges for device fabrication. Cross-linking the organic semiconductor is a viable approach, but cross-linked CTLs require additional development for practical application. Here a facile in situ strategy to prepare a cross-linked electron transport layer (ETL) is demonstrated by employing a semiconducting cross-linker composed of perylenediimidediazide, together with the fullerene (C-60) derivative coded as PCBM. Varying the PCBM ratio the cross-linking conditions affords a tunable ETL that exhibits solvent tolerance, suitable electron mobility (>10(-4) cm(2) V-1 s(-1)), and hydrophobicity at cross-linking temperatures as low as 120 degrees C. In both the n-i-p structure and the p-i-n perovskite solar cells employing our ETL, stable power generation and hysteresis-free performance are achieved. Optimized p-i-n devices with our cross-linked ETL gave power conversion efficiency of over 12% (active area of 1.07 cm(2)). These results suggest that robust n-type semiconducting films obtained with our cross-linking method are promising as ETLs in practical optoelectronic applications.