Improving the performance of GaInP solar cells through rapid thermal annealing and delta doping

Metamorphic and Lattice-Matched GaInP Rear-Heterojunction Solar Cells for Improved Performance at Elevated Temperatures

“…The optimal RTA conditions (850-1000 °C, 1-30 s) for DHs and solar cells were chosen based on maximizing the steady-state photoluminescence intensity [19]. In our previous studies, these cells showed comparable performance to metalorganic vapour-phase epitaxy (MOVPE)-grown cells [15], [19].…”

“…Another potential approach to achieve improved performance at elevated T is employing a rear-heterojunction (RHJ) configuration. Under standard conditions, RHJ cells can have a lower dark current and higher V OC than their FJ counterparts [14], [15], [16] due to the reduction of trap-assisted recombination in the space charge region. Moreover, the valence bands in phosphides have a significantly higher density of states than their corresponding conduction bands [17], [18], resulting in reduced thermal spreading of minority holes compared with electrons; i.e., at a given T, minority holes tend to occupy states close to the valence band edge.…”

Effect of Threading Dislocations on GaInP Front- and Rear-Junction Solar Cells Grown on Si

“…The RHJ cells consisted of a 20 nm n-AlInP window (n = 5 × 10 18 cm −3 ), a 500-810 nm n-GaInP emitter (n = 1 × 10 17 cm −3 ), and a 100 nm p-AlGaInP BSF (p = 1 × 10 17 cm −3 ), with the junction at the emitter/BSF interface. The RHJ AlInP window had 5× higher doping than FJs to improve front-surface passivation, which was vital for high-performance GaInP RHJs [19], and this higher doping was achieved by the addition of four delta-doped layers of Si (0.01 monolayers each). Compared to the n-AlInP barriers for the n-GaInP DH, the n-AlInP window on the RHJs is much thinner, so higher doping was needed to provide a comparable level of surface passivation.…”

“…A two-layer antireflection coating (ARC) of TiO x /SiO x was sputtered onto the FJs, while no ARC was applied to the RHJs. We performed postgrowth rapid thermal annealing (RTA) to improve the phosphide material quality of both DHs and cells, as reported previously [19], with temperatures of 750-1000 °C and annealing times of 10-120 s. Cells were processed using standard lithography and metal deposition techniques, with device dimensions of 1.1 mm × 1.1 mm; metal contacts were deposited on the top surfaces of the n + -GaAs and p + -GaAs contact layers shown in Fig. 2.…”

“…The standard GaInP cell design is the FJ n + /p or p + /n cell, which consists of a thin n + -or p + -emitter on a thick p-or n-type base to maximize photocarrier generation and collection near the space charge region (SCR). However, to date, the highest efficiency GaInP cells lattice-matched on GaAs have used a rear-heterojunction (RHJ) n-on-p design, in which a thick (>800 nm), lightly doped (1-5 × 10 17 cm −3 ) n-type GaInP absorber forms a junction on top of p-AlGaInP [17], [18], [19]. Due to their junction placement far from the highest photocarrier region, RHJ cells require high minority carrier diffusion length to achieve similar EQE to FJs, and may be particularly sensitive to defects that lower diffusion length.…”