Recent advances in polymer/silicon heterojunction solar cells

Figure 6: J-V curve and solar cell parameters of a largearea BackPEDOT solar cell fabricated on boron-doped Czochralski-grown silicon (15.6×15.6 cm2). The cell front is conventionally processed (phosphorus diffusion, silicon nitride deposition, Ag screen printing and firing).` Figure 6 shows the J-V curve of the best cell of our first batch, fabricated on industrial boron-doped p-type Czochralski-grown silicon (cell size 15.6×15.6 cm2).
The reached efficiency of 19.5% is mainly limited by the nonoptimal phosphorus-diffused front emitter and the nonoptimized firing process. As our BackPEDOT concept works on p- as well as on n-type silicon wafers, we have also processed solar cells of the same size on phosphorusdoped n-type Czochralski-silicon wafers, resulting in maximum efficiencies of 18.4% due to shunting problems. Based on realistic estimates, we expect efficiencies >21% in the near future on p- as well as ntype silicon wafers, making the BackPEDOT cell concept potentially attractive for industrial solar cell production
6 SUMMARY
 The thickness of the native SiOx between the c-Si surface and the PEDOT:PSS plays a crucial role.
 Contact resistances which are compatible with high efficiencies have only been obtained for ultrathin native SiOx (< 1 nm).
 Two-sides heterojunction cells with n-a-Si:H as electron-collector at the front and PEDOT:PSS as hole-collector at the rear show very high Voc and  potential (> 22%). First experimental cells were, however, limited by process issues to Voc=652 Mv and  = 15.2%.
 The efficiency of BackPEDOT cells is stable during storage in darkness at ambient atmosphere if a metal foil is put on the rear, as metal foils do not transmit any humidity in contrast to evaporated metals.
 We have presented first results of our attempt to implement a PEDOT:PSS/c-Si junction into an industrial-type large-area (15.6×15.6 cm2) screenprinted c-Si solar cell. The front surface of this cell was conventionally processed by phosphorusdiffusion, silicon nitride deposition, Ag screenprinting and firing. The highest efficiency of our first batch of this industrial-type BackPEDOT cell was 19.5%, mainly limited by the conventionally processed front.
 We estimate a realistic efficiency potential >21% for the industrial version of the BackPEDOT cell on pas well as n-type silicon wafers.