Aderivedcurrent‐voltage (I‐V) characteristic forp‐nheterojunction solar cells of the form window/absorber is obtained. The development lends itself to a simple, diagrammatical interpretation of the step‐by‐step collection of the photocurrent flowing out of the base of the absorber. The resulting generalI‐Vcharacteristic under illumination is in a form useful for the design of these devices and for the interpretation of their performance.