In this paper we report on printed bulk heterojunction solar cells from poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C-61 butyric acid methyl ester (PCBM) with power efficiencies of over 4 %. Devices have been produced by doctor blading, which is a reel-to-reel compatible large-area coating technique. Devices exhibit a short-circuit current of over 11.5 mA cm(-2), a fill factor of 58 %, and an open-circuit voltage of 61.5 mV, resulting in an AM1.5 power efficiency of over 4.0 % at 25 degrees C and under 100 MW cm(-2). The mismatch factor of the solar simulator is cross-calibrated by determining the spectral quantum efficiency of organic devices as well as of a calibrated Si device, and by the combination of outdoor tests; these efficiencies are precise within less than 3 % relative variation. Although the devices are regarded as fairly optimized, analysis in terms of a one-diode equivalent circuit reveals residual losses and loss mechanisms. Most interestingly, the analysis points out the different properties of spin-coated versus bladed devices. Based on this analysis, the future efficiency potential of P3HT-PCBM solar cells is analyzed.