PEDOT:PSS-free organic photovoltaic cells using tungsten oxides as buffer layer on anodes

Performance and Uniformity Improvement in Ultrathin Cu(In,Ga)Se2 Solar Cells with a WOx Nanointerlayer at the Absorber/Transparent Back-Contact Interface

“…It is known that an increase in the R s on increasing the thickness of the WO x interlayer beyond 25 nm minutely affects the device J sc . 35 However, in ref 43, the rollover effect started appearing in light-JV curves even at room temperature on increasing the WO x interlayer thickness to ≥20 nm. On further increasing the interlayer thickness from 26 to 38 nm, the roll-over effect became even more severe, and the J sc was reduced from 8.59 to 4.62 mA cm −2 .…”

“…Both W9 and W12 have poor carrier collection at wavelengths longer than 800 nm. It is known that an increase in the R s on increasing the thickness of the WO x interlayer beyond 25 nm minutely affects the device J sc . However, in ref , the roll-over effect started appearing in light- JV curves even at room temperature on increasing the WO x interlayer thickness to ≥20 nm.…”

“…The decrease of the V oc of W9 and W12 even below the V oc of W0 indicates inferior carrier collections at the back-contact. The increased series resistance ( R s ) of a cell due to the WO x interlayer beyond a certain thickness value cannot be held responsible for the decreased V oc in W9 and W12 because the value of V oc remained almost sustained in several references on increasing the thickness of the WO x ,,, or MoO x ,, HELs. The unfavorable energy level alignment, which creates an energy barrier at the rear interface, can be a possible origin behind the reduced V oc because it will increase the carrier recombination .…”

“…CIGSe peaks marked with an asterisk in Figure 8 are in accordance with the PDF card no. 35-1102 [chemical formula: Cu(In 0.7 ,Ga 0.3 )Se 2 ]. XRD reflections marked with a diamond are emerging from the ITO back-contact, which is in agreement with the PDF card number 06-0416 (chemical formula: In 2 O 3 ).…”

“…In contrast to MoO x whose potential in improving the performance of organic, CIGSe (bulk and ultrathin), and CdTe solar cells has already been reported, the role of WO x as an anodic buffer layer/HEL in bulk or ultrathin CIGSe solar cells is unknown. A WO x layer has been previously used as a HEL in OPVs, such as bulk heterojunction and tandem solar cells, because it suppresses the carrier recombination near the anode because of efficient hole collection. − In addition to this, a WO x layer has also been used as hole selective contact in crystalline , and in amorphous-silicon solar cells . On the basis of the property of raising the Φ of the ITO back-contact, WO x has been used to provide the ohmic contact between CdTe and low Φ metal electrodes, such as Mo and Ni .…”