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Temperature difference and its duration are two main factors that affect thermoelectric performance. One can obtain the desired temperature distributions by manipulating heat flow directions; however, it is generally neglected when designing thermoelectric generators (TEGs). In this study, thermal rectifiers work in forward directions to produce in-plane temperature differences (ΔTh), where hot and cold zones are, respectively, provided by the small terminals of rectifiers and gaps between these areas. Thermoelectric legs placed above are arranged in an "X"-shape, keep TEGs' internal resistances, and have a stable range from 0.7 to 2 Ω; even heating temperatures Th have a significant range from 30 to 80 °C. When the rectification coefficient of thermal rectifiers was 1.63 and the thickness of thermoelectric legs decreased from 1 mm to 10 μm, simulated-ΔTh in the steady state rises from 2.62 to 27.10 °C rather than falling. An experimental thermal rectifier with a PI film thickness of 25 μm demonstrates that ΔTh can reach up to 14.7 °C, and the time duration is more than 60 s, where Th and ambient are 50 and 20 °C, respectively. The maximum output power can reach up to 92.48 μW when the temperature bias between Th and ambient increases to 65.33 °C. These novel thin-TEGs with designed in-plane temperature gradient zones by asymmetric thermal rectifiers are expected to be applied in distributed sensors, wearable devices, etc. [ABSTRACT FROM AUTHOR]