Transparent-conductive-oxide-free front contacts for high-efficiency silicon heterojunction solar cells

Abstract

In order to compensate the insufficient conductance of heterojunction thin films, transparent conductive oxides (TCO) have been used for decades in both-sides contacted crystalline silicon heterojunction (SHJ) solar cells to provide lateral conduction for efficient carrier collection. In this work, we substitute the TCO layers by utilizing the lateral conduction of c-Si absorber, thereby enabling a TCO-free design. A series resistance of 0.32 Ωcm 2 and a fill factor of 80.7% were measured for a TCO-free back-junction SHJ solar cell with a conventional finger pitch of 1.8 mm, thereby proving that relying on lateral conduction in the c-Si bulk is compatible with low series resistances. Achieving high efficiencies in SHJ solar cells with TCO-free front contacts requires suppressing deterioration of the passivation quality induced by direct metal-a-Si:H contacts and in-diffusion of metal into the a-Si:H layer. We show that an ozone treatment at the a-Si:H/metal interface suppresses the metal diffusion and improves the passivation without increasing the

Controllable Simultaneous Bifacial Cu‐Plating for High‐Efficiency Crystalline Silicon Solar Cells

“…[ 48 ] This can be of special importance for the emerging BF transparent conductive oxide (TCO)‐less/free SHJ solar cell topic in recent years. [ 49,50 ] Third, in reality, the w top could be higher than the calculated value, which is more detrimental when using the hybrid finger as shown in Figure 3b. The aforementioned calculation of w top is based on the assumption that the metal surface is ideally smooth and reflective.…”

“…It has been theoretically and experimentally proven that the c-Si absorber itself could provide sufficient lateral electron transport toward the metal electrodes. [50,56] For the p-side, we calculated the diffusion length of the holes to be 1080 μm. This value is bigger than the finger gap of 915 μm in plated Cu grid, but smaller than the finger gap of 1740 μm in printed Ag grid.…”

Toward Efficiency Limits of Crystalline Silicon Solar Cells: Recent Progress in High‐Efficiency Silicon Heterojunction Solar Cells

“…In 2021, Li et al developed a TCO-free SHJ solar cell to decrease the free-carrier absorption loss caused by the TCO and lower costs. [96] This modification yielded a short-circuit current density of more than 40 mA cm −2 . In 2019, a number of groups demonstrated that SiN x /TCO composite layers at the front surface for rear-emitter SHJ solar cells can enhance the optical performance without damaging the lateral transport of carriers and the passivation.…”

Optical Optimization Potential of Transparent‐Passivated Contacts in Silicon Solar Cells

“…[ 28 ] Li et al have shown that the TCO can be completely omitted and that the c‐Si wafer can be used for lateral conduction if the contact resistance is sufficiently low. [ 29 ]…”