Recombination Behavior of Photolithography-free Back Junction Back Contact Solar Cells with Carrier-selective Polysilicon on Oxide Junctions for Both Polarities

We report on ion-implanted, inkjet patterned back junction back contact silicon solar cells with POLysilicon on Oxide (POLO) junctions for both polarities – n+ doped BSF and p+ doped emitter. The recombination behavior is investigated at two different processing stages: before and after trench separation of p+ and n+ regions within polysilicon (poly-Si). Before trench separation, we find a systematic dependence of the recombination behavior on the BSF index, i.e. the p+n+-junction meander length in the poly-Si. Obviously, recombination at the p+n+-junction in the poly-Si limits the implied open circuit voltage Voc,impl. at one sun illumination and the implied pseudo fill factor pFFimpl. to 695 mV and 80%, respectively. After trench isolation, however, Voc,impl (pFFimpl.) values increase up to 730 mV (85.5%), corresponding to a pseudo-efficiency of 26.2% for an assumed short circuit current density Jsc of 42 mA/cm2. We demonstrate a photolithography-free back junction back contacted solar cell with p-type and n-type POLO junctions with an in-house measured champion efficiency of 23.9% on a designated area of 3.97 cm2. This efficiency is mainly limited by the imperfect passivation in the undoped trench regions and at the undoped front side.EU/FP7/60849

Two-level Metallization and Module Integration of Point-contacted Solar Cells

AbstractWe present a module integration process for back junction back contact (BJBC) solar cells featuring point contacts to the back surface field (BSF). We apply two metallization layers. A first metal layer of aluminum is deposited onto the rear side of the cell and carries the current extracted from the polarity with the larger surface area fraction, e.g. from the emitter. The second metallization layer is an Al layer on a transparent substrate that we laser-weld to the small and point-shaped regions of the other polarity, e.g. the BSF region. We use a polymer for insulation between the two metal layers. The Al layer on the substrate also serves for cell interconnection, i.e., it enables module integration. Such an interconnection structure halves the fill factor losses due to the metallization. First proof-of-principle modules show a shunt free interconnection, no laser-induced damage, and an energy conversion efficiency of up to 20.7%

Atomic-layer-deposited aluminum oxide for the surface passivation of high-efficiency silicon solar cells

We present independently confirmed efficiencies above 20% for PERC-type solar cells with the point-contacted rear being either passivated by atomic-layer-deposited Al2O3 or by stacks consisting of an ultrathin Al2O3 film and a thicker PECVD-SiOx layer. Internal quantum efficiency measurements reveal that the effective rear surface recombination velocities of the single-layer Al2O 3-passivated cells are comparable to those measured on reference cells passivated by an aluminum-annealed thermal SiO2, while those of the Al2O3/SiOx-passivated cells are even lower. Very low effective rear surface recombination velocities of only 70 cm/s are reported for the Al2O3/SiOx stacks, including metalized areas on the cell rear

ITO-free metallization for interdigitated back contact silicon heterojunction solar cells

We report on two different approaches to fabricate interdigitated back contact silicon heterojunction solar cells without using indium tin oxide (ITO). The standard ITO/Ag backend is either modified by replacing ITO with aluminum-doped zinc oxide (AZO) or completely replaced by a sole aluminum (Al) layer. The very transparent AZO enhances the optical properties at the rear side resulting in an increase in short-circuit current density. The efficiency of the AZO cells remains on the level of the ITO ones, as the fill factor drops slightly. On the contrary, the contact resistivity of annealed Al, in comparison to ITO and AZO, to the emitter and BSF layers is much lower, thus the fill factor is increased. Despite lower open circuit voltages, cells with Al achieve efficiencies of up 22 %, a gain of 0.5 %abs compared to the ITO reference

Optimized Metallization for Interdigitated Back Contact Silicon Heterojunction Solar Cells

We report on the design and manufacturing of interdigitated back contact cells based on the silicon heterojunction technology. The influence of geometry and overlap of the doped amorphous silicon layers forming the contact fingers on device performance have been investigated by simulation. Two contact formation concepts, with and without a TCO interlayer - an indium tin oxide/silver (ITO/Ag) stack, and a direct aluminum (Al) metallization - are experimentally evaluated. The former retains good passivation but leads to a too high contact resistivity, the latter shows the opposite behavior, but yields a slight benefit in terms of overall performance achieving more than 20% of efficiency. We show that in this case a contact system is formed whose properties can be tuned by annealing, enabling a trade-off between V-OC and FF. [GRAPHICS] . Structure of the presented solar cell; a SiNX layer covers the front side, the rear side is passivated by overlapping layer stacks of intrinsic and doped amorphous silicon, the latter are contacted by aluminum

Atomic-layer-deposited aluminum oxide for the surface passivation of high-efficiency silicon solar cells

\u3cp\u3eWe present independently confirmed efficiencies above 20% for PERC-type solar cells with the point-contacted rear being either passivated by atomic-layer-deposited Al\u3csub\u3e2\u3c/sub\u3eO\u3csub\u3e3\u3c/sub\u3e or by stacks consisting of an ultrathin Al\u3csub\u3e2\u3c/sub\u3eO\u3csub\u3e3\u3c/sub\u3e film and a thicker PECVD-SiO\u3csub\u3ex\u3c/sub\u3e layer. Internal quantum efficiency measurements reveal that the effective rear surface recombination velocities of the single-layer Al\u3csub\u3e2\u3c/sub\u3eO \u3csub\u3e3\u3c/sub\u3e-passivated cells are comparable to those measured on reference cells passivated by an aluminum-annealed thermal SiO\u3csub\u3e2\u3c/sub\u3e, while those of the Al\u3csub\u3e2\u3c/sub\u3eO\u3csub\u3e3\u3c/sub\u3e/SiOx-passivated cells are even lower. Very low effective rear surface recombination velocities of only 70 cm/s are reported for the Al\u3csub\u3e2\u3c/sub\u3eO\u3csub\u3e3\u3c/sub\u3e/SiO\u3csub\u3ex\u3c/sub\u3e stacks, including metalized areas on the cell rear.\u3c/p\u3