Influence of the Bulk Resistivity on Silicon Heterojunction Solar Cells and Module Reliability

Abstract

Recent developments in industry on surface passivation open the possibility of using less doped substrates in silicon solar cells. We investigate how the bulk resistivity affects the performance of silicon cells and the reliability of modules. Herein, n‐ and p‐type silicon heterojunction cells with bulk resistivities between 3 and 15 000 Ωcm are studied. We measure the current–voltage characteristics of n‐type cells across the resistivity range, and we find comparable responses to illumination intensities between 0.1 and 1 suns. The cells with bulk resistivities over 1000 Ωcm show breakdown voltages larger than −1000 V, almost two orders of magnitude higher than in typical commercial cells. Although modules have bypass‐diodes to prevent cells from going into breakdown, higher breakdown voltages can improve the reliability of modules in case of bypass‐diode failure and reduce the module cost by easing the number of bypass‐diodes required. Finally, the cells have been submitted to light soaking. The float‐zone p‐type cells with bulk resistivities over 10 000 Ωcm are less sensitive to light‐induced degradation than cells with bulk resistivities below 10 Ωcm. The former show to recover few hours after light soaking, while the latter recover only after dark annealing.

Closing the gap between n‐ and p‐type silicon heterojunction solar cells: 24.47% efficiency on lightly doped Ga wafers

“…However, the strong carrier injection at mpp (around 2 × 10 15 cm −3 in these well passivated devices) actually provides enough carriers for the effective resistivity to be significantly reduced down to a few Ω·cm, thereby preventing from any significant Rs‐induced FF loss. SHJ cells made on very high resistivity n‐type wafers were previously reported to retain very good FF even at low illumination levels (down to 0.2 Suns), owing once more to the outstanding passivation properties of the SHJ cell, enabling significant injection in the substrate even under relatively low illumination levels 12,19 . Further work is required to assess whether this statement also holds true for high resistivity p‐type SHJ cells.…”

“…SHJ cells made on very high resistivity n-type wafers were previously reported to retain very good FF even at low illumination levels (down to 0.2 Suns), owing once more to the outstanding passivation properties of the SHJ cell, enabling significant injection in the substrate even under relatively low illumination levels. 12,19 Further work is required to assess whether this statement also holds true for high resistivity ptype SHJ cells. Note that the pFF drops like the FF with a smaller pFF-FF gap for low FF p-type cells, as shown in Figure 4.…”

Low Breakdown Voltage Solar Cells for Shading Tolerant Photovoltaic Modules

“…The first module, referred to as IBC, was built with commercially available 5-in c-Si IBC solar cells with a BDV close to 3 V. 51 The second module, referred to as FBC, was built with 5-in front/back-contacted c-Si Al-BSF solar cells with a BDV larger than 10 V. The external parameters of FBC and IBC cells are listed in Table S2. Even though commercially available FBC solar cells based on passivated emitter and rear contact (PERC) and heterojunction (HJT) technologies can achieve higher efficiencies than Al-BSF, these cells are generally manufactured using 6-in (or larger) wafers and also present BDVs larger than 10 V. 19,52 Taking this into account, it is reasonable to assume that the conclusions from our experiments are also applicable to newer FBC cell technologies.…”

Temperature profiles of field-aged photovoltaic modules affected by optical degradation

“…The resistivity ( ρ ) of a material determines how easily electricity can flow through it. In the case of PV modules, the solar cells are made of semiconducting materials with specific resistivity values [ 45 ]. When a hotspot occurs in a PV module, the ρ can increase.…”