An efficient ITO-free top-illuminated organic photovoltaic (TOPV) based on small molecular planar heterojunction was achieved by spinning a buffer layer of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), on the <svg style="vertical-align:-4.10043pt;width:65.112503px;" id="M1" height="16.5375" version="1.1" viewBox="0 0 65.112503 16.5375" width="65.112503" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns="http://www.w3.org/2000/svg"> <g transform="matrix(.017,-0,0,-.017,.062,11.363)"><path id="x41" d="M673 0h-245v28q47 6 58 16t1 39l-55 154h-213q-31 -87 -36 -129q-16 -47 -5 -61t68 -19v-28h-226v28q50 7 68.5 23.5t43.5 80.5l214 524l24 9l193 -536q23 -63 41.5 -79.5t68.5 -21.5v-28zM418 280l-81 255h-2q-74 -197 -101 -255h184z" /></g><g transform="matrix(.017,-0,0,-.017,11.588,11.363)"><path id="x67" d="M463 437l5 -8q-21 -38 -45 -51l-57 3q30 -35 30 -88q0 -76 -52.5 -118t-122.5 -42q-24 0 -51 5q-30 -21 -30 -42q0 -16 16 -27t47 -11q19 0 54 0.5t52 0.5q36 0 65.5 -8t53.5 -36t24 -74q0 -77 -75 -137.5t-174 -60.5q-79 0 -126 37.5t-48 84.5q0 32 24 56q21 21 83 70
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q0 16 13.5 31.5t28.5 15.5q12 0 17 -11q5 -10 25 -10q22 0 57.5 36t89.5 111l-40 108q-22 58 -36 58q-21 0 -67 -57l-19 20q81 107 125 107q17 0 30 -22t39 -88l22 -55q68 92 108.5 128.5t74.5 36.5q20 0 32.5 -14t12.5 -30z" /></g> </svg> anode. The PEDOT:PSS thin film separates the active layer far from the Ag anode to prevent metal quenching and redistributes the strong internal optical field toward dissociated interface. The thickness and morphology of this anodic buffer layer are the key factors in determining device performances. The uniform buffer layer contributes a large short-circuit current and open-circuit voltage, benefiting the final power conversion efficiency (PCE). The TOPV device with an optimal PEDOT:PSS thickness of about 30 nm on <svg style="vertical-align:-4.10043pt;width:65.112503px;" id="M2" height="16.5375" version="1.1" viewBox="0 0 65.112503 16.5375" width="65.112503" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns="http://www.w3.org/2000/svg"> <g transform="matrix(.017,-0,0,-.017,.062,11.363)"><use xlink:href="#x41"/></g><g transform="matrix(.017,-0,0,-.017,11.588,11.363)"><use xlink:href="#x67"/></g><g transform="matrix(.017,-0,0,-.017,19.543,11.363)"><use xlink:href="#x2D"/></g><g transform="matrix(.017,-0,0,-.017,25.595,11.363)"><use xlink:href="#x41"/></g><g transform="matrix(.017,-0,0,-.017,37.12,11.363)"><use xlink:href="#x67"/></g><g transform="matrix(.017,-0,0,-.017,45.075,11.363)"><use xlink:href="#x4F"/></g> <g transform="matrix(.012,-0,0,-.012,57.775,16.325)"><use xlink:href="#x1D465"/></g> </svg> anode exhibits the maximum PCE of 1.49%. It appreciates a 1.37-fold enhancement in PCE over that of TOPV device without buffer layer.